CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 37,704	$ 29,687	$ 95,355	$ (15,558)
Other comprehensive income, net of tax:
Comprehensive income (loss), net of tax	$ 37,704	$ 29,687	$ 95,355	$ (15,558)