Derivatives and hedging activities (Details) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2013 Interest Rate Swaps USD ($)	Dec. 31, 2013 Interest Rate Swaps EUR (€)	Dec. 31, 2012 Interest Rate Swaps USD ($)	Dec. 31, 2012 Interest Rate Swaps EUR (€)	Dec. 31, 2013 Non-designated hedges Interest Rate Options USD ($)	Dec. 31, 2013 Non-designated hedges Interest Rate Options EUR (€)	Dec. 31, 2012 Non-designated hedges Interest Rate Options USD ($)	Dec. 31, 2012 Non-designated hedges Interest Rate Options EUR (€)
Derivative [Line Items]
Fair value of derivatives not designated as hedges								$ 2		$ 6
Notional amount of derivatives not designated as hedges				63,700	137,469	104,259	142,094	59,080	73,344	53,760	76,469
Amount accounted for in other comprehensive income/(loss), which is expected to be reclassified to interest expense in the next 12 months				3,003
Amounts recorded in other comprehensive income/(loss)	(1,016)	(806)	2,748
Fair value of derivatives in a net liability position	(4,890)	(8,879)
Assets required to settle obligations under derivatives with credit-risk-related contingent features upon breach of provisions, termination value	4,899	8,946
Fair value of non-derivative hedging instruments	$ 26,249	$ 44,166