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)	$ 123,385	$ 26,762	$ (14,746)
Other comprehensive (loss) income:
Reclassification adjustment for gains on sales of assets included in net income	0	435	0
Foreign currency translation	(87)	603	(355)
Total other comprehensive (loss) income	(87)	1,038	(355)
Comprehensive income (loss)	$ 123,298	$ 27,800	$ (15,101)