Accumulated other comprehensive loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period, net of tax	$ (18,182)	$ (9,066)	$ (12,569)	$ (8,556)
Net current period other comprehensive loss, net of tax	(2,910)	(1,803)	(8,523)	(2,313)
Balance, end of period, net of tax	(21,092)	(10,869)	(21,092)	(10,869)
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period, net of tax	(17,149)	(8,374)	(11,834)	(8,118)
Net current period other comprehensive loss, net of tax	(1,370)	(1,850)	(6,685)	(2,106)
Balance, end of period, net of tax	(18,519)	(10,224)	(18,519)	(10,224)
Minimum pension liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period, net of tax	730	(53)	334	(210)
Net current period other comprehensive loss, net of tax	(1,101)	(28)	(705)	129
Balance, end of period, net of tax	(371)	(81)	(371)	(81)
Cash flow hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period, net of tax	(1,763)	(639)	(1,069)	(228)
Net current period other comprehensive loss, net of tax	(439)	75	(1,133)	(336)
Balance, end of period, net of tax	$ (2,202)	$ (564)	$ (2,202)	$ (564)