Derivatives and hedging activities (Details) In Thousands, unless otherwise specified	3 Months Ended			3 Months Ended	12 Months Ended				3 Months Ended
	Mar. 31, 2014 USD ($)	Mar. 31, 2013 USD ($)	Dec. 31, 2013 USD ($)	Mar. 31, 2014 Net Investment Hedging [Member] USD ($)	Dec. 31, 2013 Net Investment Hedging [Member] USD ($)	Mar. 31, 2014 Interest Rate Option [Member] Derivatives not designated as hedges USD ($)	Dec. 31, 2013 Interest Rate Option [Member] Derivatives not designated as hedges USD ($)	Dec. 31, 2013 Interest Rate Option [Member] Derivatives not designated as hedges EUR (€)	Mar. 31, 2014 Interest Rate Swap [Member] USD ($)	Mar. 31, 2014 Interest Rate Swap [Member] EUR (€)	Dec. 31, 2013 Interest Rate Swap [Member] USD ($)	Dec. 31, 2013 Interest Rate Swap [Member] EUR (€)
Derivatives, Fair Value [Line Items]
Termination costs									$ 5,162
Derivative, notional amount						58,800	59,080	73,344	172,500	75,000	63,700	137,469
Amount recorded in other comprehensive income which is expected to be reclassified to interest expense in the next 12 months									2,384
Gain/(loss) recorded in other comprehensive income/(loss)	(434)	1,111
Fair value of derivatives in a net liability position	825		4,890
Assets required to settle obligations under derivatives with credit-risk-related contingent features upon breach of provisions, termination value	762		4,899
Fair value of non-derivative hedging instruments				$ 206,725	$ 26,249