Accumulated other comprehensive income - Components of Changes in Accumulated Other Comprehensive Income (Parenthetical) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Deferred taxes recognized on related foreign currency translation adjustment	$ 0
Fair Value of Cross-Currency Swap [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gain on derivative instrument, taxes (benefit)	25,000
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gain on derivative instrument, taxes (benefit)	$ 25,000