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	$ (199,228)	$ (2,483)	$ 32,779
Unrealized (losses) gains on marketable securities:
Holding (losses) gains arising during period, net of tax	(70)	261	(4)
Reclassification adjustment for gains (losses) included in net (loss) income, net of tax	0	106	(584)
Net unrealized (losses) gains on securities	(70)	367	(588)
Total comprehensive (loss) income	$ (199,298)	$ (2,116)	$ 32,191