CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 38,169	$ 40,501	$ 93,357	$ 89,045
Other comprehensive income, net of tax
Unrealized translation adjustment	(1,395)	(111)	(1,378)	(751)
Minimum pension liability adjustments	606	994	1,767	2,982
Unrealized interest rate swap adjustments	446	(1,152)	(339)	2,150
Total other comprehensive income, net of tax	(343)	(269)	50	4,381
Comprehensive income	$ 37,826	$ 40,232	$ 93,407	$ 93,426