Accumulated other comprehensive loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period, net of tax	$ (15,438)	$ (12,641)	$ (12,569)	$ (8,556)
Net current period other comprehensive loss, net of tax	(2,744)	3,575	(5,613)	(510)
Balance, end of period, net of tax	(18,182)	(9,066)	(18,182)	(9,066)
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period, net of tax	(13,862)	(11,137)	(11,834)	(8,118)
Net current period other comprehensive loss, net of tax	(3,287)	2,763	(5,315)	(256)
Balance, end of period, net of tax	(17,149)	(8,374)	(17,149)	(8,374)
Minimum pension liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period, net of tax	251	(475)	334	(210)
Net current period other comprehensive loss, net of tax	479	422	396	157
Balance, end of period, net of tax	730	(53)	730	(53)
Cash flow hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period, net of tax	(1,827)	(1,029)	(1,069)	(228)
Net current period other comprehensive loss, net of tax	64	390	(694)	(411)
Balance, end of period, net of tax	$ (1,763)	$ (639)	$ (1,763)	$ (639)