Fair value measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Interest Rate Swap
Assets/(Liabilities)
Derivative Assets (Liabilities), at Fair Value, Net	$ (1,742)	$ 727
Interest Rate Swap | Fair Value, Inputs, Level 2
Assets/(Liabilities)
Derivative Assets (Liabilities), at Fair Value, Net	(1,742)	727
Foreign Exchange Contract
Assets/(Liabilities)
Derivative Assets (Liabilities), at Fair Value, Net	4,919	3,417
Foreign Exchange Contract | Fair Value, Inputs, Level 2
Assets/(Liabilities)
Derivative Assets (Liabilities), at Fair Value, Net	4,919	3,417
Commodity Contract
Assets/(Liabilities)
Derivative Assets (Liabilities), at Fair Value, Net	(777)	(1,333)
Commodity Contract | Fair Value, Inputs, Level 2
Assets/(Liabilities)
Derivative Assets (Liabilities), at Fair Value, Net	$ (777)	$ (1,333)