Derivatives and hedging activities - Narratives (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Loss recorded in other comprehensive income/(loss)	$ 2,342	$ 7,661
Fair value of derivatives in a net liability position	2,513		$ 3,364
Assets required to settle obligations under derivatives with credit-risk-related contingent features upon breach of provisions, termination value	2,513		3,370
Net Investment Hedging
Derivatives, Fair Value [Line Items]
Fair value of non-derivative hedging instruments	155,323		$ 153,472
Interest rate swaps
Derivatives, Fair Value [Line Items]
Amount recorded in other comprehensive income which is expected to be reclassified to interest expense in the next 12 months	$ 1,821