CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 12,132	$ 22,822	$ 11,591	$ 37,446
Other comprehensive income (loss) before taxes:
Change in fair value of interest rate swap agreements	42	(2,798)	2,144	(7,676)
Provision for income tax benefit (expense) related to components of other comprehensive income (loss)	(16)	1,063	(815)	2,916
Other comprehensive income (loss)	26	(1,735)	1,329	(4,760)
Comprehensive income (loss)	$ 12,158	$ 21,087	$ 12,920	$ 32,686