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) including noncontrolling interests in operating subsidiaries	$ 21,684	$ (54,799)	$ (157,478)
Other comprehensive income (loss):
Unrealized loss on short-term investments	(40)	40	(356)
Unrealized gain on foreign currency translation	58	77	(123)
Add: reclassification adjustment for losses included in net income	(30)	22	617
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	21,672	(54,660)	(157,340)
Net (income) loss attributable to noncontrolling interests in subsidiaries	(496)	(732)	2,558
Comprehensive income	$ 22,168	$ (53,928)	$ (159,898)