Consolidated Statements Of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (56,558)	$ 56,089	$ 117,016
Other comprehensive income (loss):
Net unrealized gains (losses) on available-for- sale securities, net of tax	(155)	1,289	(1,104)
Other comprehensive income (loss)	(155)	1,289	(1,104)
Comprehensive income (loss)	$ (56,713)	$ 57,378	$ 115,912