Accumulated other comprehensive loss - Components of Changes in Accumulated Other Comprehensive Loss (Parenthetical) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Deferred taxes recognized on related foreign currency translation adjustment	$ 0
Cross-Currency Swap and Warrants [Member] | Change in Fair Value [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Unrealized gain on cross-currency swap and warrants, net of tax	435,000
Cross-Currency Swap and Warrants [Member] | Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Unrealized gain on cross-currency swap and warrants, net of tax	$ 435,000