Annual report pursuant to Section 13 and 15(d)

EMPLOYEE BENEFIT PLANS (Details)

v2.4.1.9
EMPLOYEE BENEFIT PLANS (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
EMPLOYEE BENEFIT PLANS [Abstract]      
Percentage match of eligible employee's deferral contribution (in hundredths) 100.00%nog_PercentageEntityMatchesOfEligibleEmployeesContributions 100.00%nog_PercentageEntityMatchesOfEligibleEmployeesContributions 100.00%nog_PercentageEntityMatchesOfEligibleEmployeesContributions
Maximum percentage of eligible employee's deferral contribution matched (in hundredths) 8.00%nog_MaximumPercentageOfEligibleCompensationMatched 8.00%nog_MaximumPercentageOfEligibleCompensationMatched 8.00%nog_MaximumPercentageOfEligibleCompensationMatched
Matching contributions to the Plans $ 269,000us-gaap_DefinedContributionPlanCostRecognized $ 240,000us-gaap_DefinedContributionPlanCostRecognized $ 189,000us-gaap_DefinedContributionPlanCostRecognized