Annual report pursuant to Section 13 and 15(d)

COMMON AND PREFERRED STOCK (Details)

v2.4.1.9
COMMON AND PREFERRED STOCK (Details) (USD $)
3 Months Ended 12 Months Ended
Dec. 31, 2014
Class
Mar. 31, 2014
Sep. 30, 2013
Dec. 31, 2014
Class
Dec. 31, 2013
Dec. 31, 2012
May 31, 2011
COMMON AND PREFERRED STOCK [Abstract]              
Total shares of preferred and common stock authorized for issuance (in shares) 100,000,000nog_StockSharesAuthorized     100,000,000nog_StockSharesAuthorized      
Number of classes of shares 2nog_NumberOfClassesOfShares     2nog_NumberOfClassesOfShares      
Common stock, shares authorized (in shares) 95,000,000us-gaap_CommonStockSharesAuthorized     95,000,000us-gaap_CommonStockSharesAuthorized 95,000,000us-gaap_CommonStockSharesAuthorized    
Common stock, par value (in dollars per share) $ 0.001us-gaap_CommonStockParOrStatedValuePerShare     $ 0.001us-gaap_CommonStockParOrStatedValuePerShare $ 0.001us-gaap_CommonStockParOrStatedValuePerShare    
Preferred stock, shares authorized (in shares) 5,000,000us-gaap_PreferredStockSharesAuthorized     5,000,000us-gaap_PreferredStockSharesAuthorized 5,000,000us-gaap_PreferredStockSharesAuthorized    
Preferred stock, par value (in dollars per share) $ 0.001us-gaap_PreferredStockParOrStatedValuePerShare     $ 0.001us-gaap_PreferredStockParOrStatedValuePerShare $ 0.001us-gaap_PreferredStockParOrStatedValuePerShare    
Changes in number of common stock shares [Roll forward]              
Beginning Balance (in shares)   61,858,199us-gaap_CommonStockSharesOutstanding   61,858,199us-gaap_CommonStockSharesOutstanding 63,532,622us-gaap_CommonStockSharesOutstanding 63,330,421us-gaap_CommonStockSharesOutstanding  
Stock Based Compensation (in shares)       0us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross 57,371us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross 53,140us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross  
Stock Options Exercised (in shares)       100,000us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised 10,091us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised 10,500us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised  
Restricted Stock Grants (in shares)       299,416us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross 353,596us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross 837,239us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross  
Stock repurchase (in shares) (134,988)us-gaap_StockRepurchasedAndRetiredDuringPeriodShares (1,018,897)us-gaap_StockRepurchasedAndRetiredDuringPeriodShares (2,036,383)us-gaap_StockRepurchasedAndRetiredDuringPeriodShares (1,153,885)us-gaap_StockRepurchasedAndRetiredDuringPeriodShares (2,036,383)us-gaap_StockRepurchasedAndRetiredDuringPeriodShares 0us-gaap_StockRepurchasedAndRetiredDuringPeriodShares  
Other Surrenders (in shares)       (79,461)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited (59,098)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited (698,678)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited  
Other (in shares)       42,443us-gaap_StockIssuedDuringPeriodSharesOther 0us-gaap_StockIssuedDuringPeriodSharesOther 0us-gaap_StockIssuedDuringPeriodSharesOther  
Ending balance (in shares) 61,066,712us-gaap_CommonStockSharesOutstanding     61,066,712us-gaap_CommonStockSharesOutstanding 61,858,199us-gaap_CommonStockSharesOutstanding 63,532,622us-gaap_CommonStockSharesOutstanding  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock Based Compensation (in shares)       0us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross 57,371us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross 53,140us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross  
Stock options exercised (in shares)       100,000us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised 10,091us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised 10,500us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised  
Fair value of common stock issued, share based compensation           $ 1,300,000us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation  
Stock Activity [Abstract]              
Common stock surrendered by certain employees to cover tax obligations (in shares)       43,835us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation 16,585us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation 70,128us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation  
Fair value of common stock surrendered by certain employees to cover tax obligations       587,000us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardForfeitures 253,000us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardForfeitures 1,500,000us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardForfeitures  
Common stock surrendered by certain employees related to termination of employment (in shares)         39,049nog_CommonStockForfeitedOrSurrenderedByCertainEmployeesRelatedToTerminationOfEmployment 628,550nog_CommonStockForfeitedOrSurrenderedByCertainEmployeesRelatedToTerminationOfEmployment  
Share-based compensation, market value of common stock issued, minimum (in dollars per share)           $ 19.34nog_StockIssuedDuringPeriodValueShareBasedCompensationPerShareMinimum  
Share-based compensation, market value of common stock issued, maximum (in dollars per share)           $ 24.89nog_RangeOfPerShareValueCommonStockIssuedMaximum  
Share-based compensation expense           500,000us-gaap_AllocatedShareBasedCompensationExpense  
Stock Repurchase Program [Abstract]              
Stock repurchase program, amount approved             150,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1
Stock repurchase (in shares) 134,988us-gaap_StockRepurchasedAndRetiredDuringPeriodShares 1,018,897us-gaap_StockRepurchasedAndRetiredDuringPeriodShares 2,036,383us-gaap_StockRepurchasedAndRetiredDuringPeriodShares 1,153,885us-gaap_StockRepurchasedAndRetiredDuringPeriodShares 2,036,383us-gaap_StockRepurchasedAndRetiredDuringPeriodShares 0us-gaap_StockRepurchasedAndRetiredDuringPeriodShares  
Treasury stock, repurchased and retired 1,800,000us-gaap_TreasuryStockRetiredCostMethodAmount 13,700,000us-gaap_TreasuryStockRetiredCostMethodAmount 26,100,000us-gaap_TreasuryStockRetiredCostMethodAmount        
Performance Equity Awards [Member]              
Stock Activity [Abstract]              
Share-based compensation expense       600,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
     
Performance Equity Awards [Abstract]              
Vesting period       3 years      
Maximum amount earned by participants on performance awards       3,100,000nog_MaximumAmountOfPerformanceSharesIssuable
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
     
Performance Equity Awards [Member] | Minimum [Member]              
Performance Equity Awards [Abstract]              
Participants earning percentage (in hundredths)       0.00%nog_PercentageOfRangeOnBaseSalariesSettledInRestrictedShares
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
     
Performance Equity Awards [Member] | Maximum [Member]              
Performance Equity Awards [Abstract]              
Participants earning percentage (in hundredths)       180.00%nog_PercentageOfRangeOnBaseSalariesSettledInRestrictedShares
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
     
Director [Member]              
Changes in number of common stock shares [Roll forward]              
Stock Options Exercised (in shares)       100,000us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
10,091us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
10,500us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock options exercised (in shares)       100,000us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
10,091us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
10,500us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
 
Shares surrendered to cover aggregate exercise price       35,626nog_SharesSurrenderedToCoverAggregateExercisePrice
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
3,464nog_SharesSurrenderedToCoverAggregateExercisePrice
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
   
Aggregate exercise price of stock surrendered       518,000nog_AggregateExercisePriceOfStockSurrendered
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
52,000nog_AggregateExercisePriceOfStockSurrendered
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
   
Chief Executive Officer [Member]              
Changes in number of common stock shares [Roll forward]              
Stock Based Compensation (in shares)         57,371us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefExecutiveOfficerMember
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock Based Compensation (in shares)         57,371us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefExecutiveOfficerMember
   
Fair value of common stock issued, share based compensation         $ 825,000us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefExecutiveOfficerMember