Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net income	$ 81,678	$ 57,217	$ 57,303
Foreign currency translation adjustments:
Foreign currency translation adjustments during the period	(8,481)	(16,424)	(25,800)
Reclassification adjustments for losses included in net income	71	1,954	4,400
Interest rate swap agreement:
Unrealized net losses		(30)	(152)
Reclassification adjustments for losses included in net income		333	465
Income taxes		(110)	(109)
Actuarial (loss)/gain
Actuarial (loss)/gain arising during the period	(3,192)	3,970	(18,338)
Amortization to net income of net actuarial loss	1,152	1,295	802
Prior service cost
Amortization to net income of net prior service cost	52	52	50
Lump-sum pension payout			7,170
Income taxes	327	(1,508)	5,493
Comprehensive income	$ 71,607	$ 46,749	$ 31,284