Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 19,386	$ 21,291
Other comprehensive income (loss) before taxes:
Change in fair value of interest rate swap agreements	1,673	2,881
Provision for income tax benefit (expense) related to components of other comprehensive income (loss)	(636)	(1,094)
Other comprehensive income (loss)	1,037	1,787
Comprehensive income (loss)	$ 20,423	$ 23,078