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Segment Reporting - Revenue by Business Segments (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Segment Reporting, Revenue Reconciling Item [Line Items]    
Total revenues $ 8,299us-gaap_Revenues $ 13,756us-gaap_Revenues
Product Sales and Services [Member]    
Segment Reporting, Revenue Reconciling Item [Line Items]    
Total revenues 5,928us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= nrthf_ProductSalesAndServicesMember		 13,544us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= nrthf_ProductSalesAndServicesMember
Technology Licensing [Member]    
Segment Reporting, Revenue Reconciling Item [Line Items]    
Total revenues 615us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= nrthf_TechnologyLicensingMember		 11us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= nrthf_TechnologyLicensingMember
Technology Development [Member]    
Segment Reporting, Revenue Reconciling Item [Line Items]    
Total revenues $ 1,756us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= nrthf_TechnologyDevelopmentMember		 $ 201us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= nrthf_TechnologyDevelopmentMember