Financial instruments - after tax (gain)/loss reclassified from accumulated other comprehensive income into income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivatives Fair Value [Line Items]
Derivatives qualifying as hedges, net of tax	$ 0	$ 381	$ 6,876
Interest Rate Swap
Derivatives Fair Value [Line Items]
Derivatives qualifying as hedges, net of tax	0	0	7,032
Foreign Currency Exchange Contracts
Derivatives Fair Value [Line Items]
Derivatives qualifying as hedges, net of tax	$ 0	$ 381	$ (156)