Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income	$ 23,443	$ 38,716	$ 31,807	$ 19,743	$ 20,704	$ 42,744	$ 34,374	$ 23,791	$ 113,709	$ 121,613	$ 111,061
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge									862	862	862
Foreign currency translation adjustment									(2,863)	237	615
Amortization of pension related costs, net of tax:
Actuarial loss (net of income tax of $48 for the year ended December 31, 2012)									0	80	0
Settlement of pension plan (net of income tax of $840 for the year ended December 31, 2012)									0	1,406	0
Actuarial pension loss (net of income tax of $649 for the year ended December 31, 2011)									0	0	(1,086)
Other comprehensive income (loss), net of tax									(2,001)	2,585	391
Comprehensive income									$ 111,708	$ 124,198	$ 111,452