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Net Loss per Share - Additional Information (Detail)
Mar. 31, 2015
Dec. 31, 2014
Apr. 16, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Stock option outstanding     367,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
Private Placement [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Stock option outstanding 367,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_PrivatePlacementMember		    
2014 NPS Corp [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Stock option outstanding 2,408,261us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nrthf_TwoThousandFourteenNorthernPowerSystemsCorpPlanMember		    
Mira III Stock Option Awards [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Stock option outstanding 35,938us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nrthf_NorthernPowerSystemsIncStockOptionAwardsMember		   35,938us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nrthf_NorthernPowerSystemsIncStockOptionAwardsMember
Stock option outstanding 35,938us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nrthf_NorthernPowerSystemsIncStockOptionAwardsMember		 35,938us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nrthf_NorthernPowerSystemsIncStockOptionAwardsMember