Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net Loss Attributable to Common Stockholders	$ (9,527,000)	$ (46,235,000)	$ (15,635,000)	$ (70,450,000)
Other comprehensive loss, net of tax:
Unrealized loss on short-term investments, net of tax	(7,000)	0	(7,000)	0
Other comprehensive loss, net of tax:	(7,000)		(7,000)
Comprehensive Net Loss	$ (9,534,000)	$ (46,235,000)	$ (15,642,000)	$ (70,450,000)