CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 18,111	$ 26,505	$ 55,557	$ 55,253
Other comprehensive income (loss) before taxes:
Change in fair value of interest rate swap agreements	4,197	(4,221)	(3,479)	(4,271)
Provision for income tax benefit (expense) related to components of other comprehensive income (loss)	(1,595)	1,604	1,322	1,623
Other comprehensive income (loss)	2,602	(2,617)	(2,157)	(2,648)
Comprehensive income (loss)	$ 20,713	$ 23,888	$ 53,400	$ 52,605