Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 25,285	$ 39,365	$ 35,400	$ 23,110	$ 23,443	$ 38,716	$ 31,807	$ 19,743	$ 123,160	$ 113,709	$ 121,613
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									861	862	862
Foreign currency translation adjustment									(1,615)	(2,863)	237
Amortization of pension related costs, net of tax:
Actuarial loss (net of income tax of $48 for the year ended December 31, 2012)									0	0	80
Settlement of pension plan (net of income tax of $840 for the year ended December 31, 2012)									0	0	1,406
Other comprehensive income (loss), net of tax									(754)	(2,001)	2,585
Comprehensive income									$ 122,406	$ 111,708	$ 124,198