Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income	$ 102,450	$ 81,678	$ 57,217
Foreign currency translation adjustments:
Foreign currency translation adjustments during the period	22,250	(8,481)	(16,424)
Reclassification adjustments for losses included in net income		71	1,954
Interest rate swap agreement:
Unrealized net losses			(30)
Reclassification adjustments for losses included in net income			333
Income taxes			(110)
Actuarial gain/(loss)
Actuarial gain/(loss) arising during the period	461	(3,192)	3,970
Amortization to net income of net actuarial loss	1,400	1,152	1,295
Prior service cost
Amortization to net income of net prior service cost	52	52	52
Income taxes	(871)	327	(1,508)
Comprehensive income	$ 125,742	$ 71,607	$ 46,749