CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest [Abstract]
Net income	$ 15,858	$ 17,851	$ 27,634	$ 28,297
Foreign currency translation adjustment	4,909	3,340	(1,251)	(595)
Unrealized gain (loss) on defined benefit plan, net of tax	4,448	(1,816)	2,635	(550)
Unrealized foreign currency gain (loss), net of tax	397	372	(101)	450
Comprehensive income	25,612	19,747	28,917	27,602
Less: Comprehensive income attributable to noncontrolling interest	(780)	(466)	(1,424)	(710)
Total comprehensive income attributable to common stockholders	$ 24,832	$ 19,281	$ 27,493	$ 26,892