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Line of credit - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
1 Months Ended
Mar. 31, 2014
Line of Credit Facility [Line Items]  
Line of Credit Facility, Interest Rate During Period 3.00%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod
Line of Credit Facility, Expiration Date Jun. 30, 2016
Letter of Credit  
Line of Credit Facility [Line Items]  
Long-term Line of Credit 5.0us-gaap_LineOfCredit
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_LetterOfCreditMember