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
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 34,125	$ 40,501	$ 34,670	$ 13,874	$ 32,925	$ 36,764	$ 27,029	$ 15,112	$ 123,170	$ 111,830	$ 108,996
Other comprehensive income (loss), net of tax:
Unrealized translation adjustment									(901)	1,567	(2,143)
Minimum pension liability adjustments									13,194	(4,645)	(20,285)
Unrealized interest rate swap adjustments									1,584	5,719	9,189
Total other comprehensive income (loss), net of tax									13,877	2,641	(13,239)
Comprehensive income									$ 137,047	$ 114,471	$ 95,757