Comprehensive income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Pension Liability Adjustment, Other comprehensive income (loss):
Pension Liability Adjustment, Balance at Beginning of the Period	$ 1,523	$ 497
Pension Liability Adjustment, Other comprehensive income (loss) before reclassifications, net of taxes	0	1,110
Pension Liability Adjustment, Total other comprehensive loss before reclassifications, net of taxes	1,523	1,607
Pension Liability Adjustment, Net amount reclassified to earnings	(136)	(84)
Pension Liability Adjustment, Balance at End of the Period	1,387	1,523
Fair Value of Derivatives, Other comprehensive income (loss):
Fair Value of Derivatives, Balance at Beginning of the Period	(165)	(337)
Fair Value of Derivatives, Other comprehensive income (loss) before reclassifications, net of taxes	(90)	(51)
Fair Value of Derivatives, Total other comprehensive loss before reclassifications, net of taxes	(255)	(388)
Fair Value of Derivatives, Net amount reclassified to earnings	(63)	223
Fair Value of Derivatives, Balance at End of the Period	(318)	(165)
Foreign Currency Translation Adjustment, Other comprehensive income (loss):
Foreign Currency Translation Adjustment, Balance at Beginning of the Period	(1,442)	(447)
Foreign Currency Translation Adjustment, Other comprehensive income (loss) before reclassifications, net of taxes	49	(995)
Foreign Currency Translation Adjustment, Total other comprehensive loss before reclassifications, net of taxes	(1,393)	(1,442)
Foreign Currency Translation Adjustment, Net amount reclassified to earnings	0	0
Foreign Currency Translation Adjustment, Balance at End of the period	(1,393)	(1,442)
Accumulated Other Comprehensive Income (loss), Other comprehensive income (loss):
Accumulated Other Comprehensive Income (loss), Balance at Beginning of the period	(84)	(287)
Accumulated Other Comprehensive Income (loss), Other comprehensive income (loss) before reclassifications, net of taxes	(41)	64
Accumulated Other Comprehensive Income (loss), Total other comprehensive loss before reclassifications, net of taxes	(125)	(223)
Accumulated Other Comprehensive Income (loss), Net amount reclassified to earnings	(199)	139
Accumulated Other Comprehensive Income (loss), Balance at End of the period	$ (324)	$ (84)