Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (126,817)	$ (69,707)	$ 26,144
Other comprehensive (loss) income:
Unrealized loss on marketable securities	0	0	(5,485)
Reclassification of other-than-temporary loss on marketable securities included in net income	0	0	5,485
Comprehensive (loss) income	$ (126,817)	$ (69,707)	$ 26,144