Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidated Statements of Comprehensive Income [Abstract]
Net income (loss)	$ 89,101	$ 76,254	$ 89,929
Other comprehensive income (loss) before taxes:
Change in fair value of interest rate swap agreements	2,722	(4,019)	5,914
Change in pension actuarial income (loss)	(258)	(508)
Total other comprehensive income (loss) before taxes	2,464	(4,527)	5,914
Provision for income tax benefit (expense) related to components of other comprehensive income (loss)	(937)	1,720	(2,247)
Other comprehensive income (loss)	1,527	(2,807)	3,667
Comprehensive income (loss)	$ 90,628	$ 73,447	$ 93,596