Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 681,313	$ (96,692)	$ (153,524)
Other comprehensive income (loss):
Net unrealized gain (loss) on available-for-sale investments, net of tax	(2,975)	(533)	79
Net foreign currency translation gain (loss)	(1,230)	785	(272)
Other comprehensive income (loss), net of tax	(4,205)	252	(193)
Comprehensive income (loss)	$ 677,108	$ (96,440)	$ (153,717)