Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest
Balance at beginning of year (in shares) at Dec. 31, 2017		65,297
Balance at beginning of year at Dec. 31, 2017	$ 349,493	$ 66	$ 1,551,728	$ (1,204,519)	$ (409)	$ 2,627
Adjustment to accumulated deficit due to adoption of ASC 606	29,037			29,037
Issuance of common stock pursuant to equity award plans (in shares)		514
Issuance of common stock pursuant to equity award plans	5,679	$ 1	5,678
Stock-based compensation expense	10,980		10,980
Other comprehensive income (loss)	(392)				(392)
Net (loss) income	(84,510)			(84,178)		(332)
Change in noncontrolling interest	(119)					(119)
Balance at end of the year (in shares) at Mar. 31, 2018		65,811
Balance at end of the year at Mar. 31, 2018	310,168	$ 67	1,568,386	(1,259,660)	(801)	2,176
Balance at beginning of year (in shares) at Dec. 31, 2017		65,297
Balance at beginning of year at Dec. 31, 2017	349,493	$ 66	1,551,728	(1,204,519)	(409)	2,627
Net (loss) income	(261,658)
Balance at end of the year (in shares) at Sep. 30, 2018		66,434
Balance at end of the year at Sep. 30, 2018	166,928	$ 67	1,601,950	(1,437,157)	(437)	2,505
Balance at beginning of year (in shares) at Mar. 31, 2018		65,811
Balance at beginning of year at Mar. 31, 2018	310,168	$ 67	1,568,386	(1,259,660)	(801)	2,176
Issuance of common stock pursuant to equity award plans (in shares)		143
Issuance of common stock pursuant to equity award plans	2,543		2,543
Stock-based compensation expense	13,214		13,214
Other comprehensive income (loss)	127				127
Net (loss) income	(105,971)			(106,194)		223
Change in noncontrolling interest	(20)					(20)
Balance at end of the year (in shares) at Jun. 30, 2018		65,954
Balance at end of the year at Jun. 30, 2018	220,061	$ 67	1,584,143	(1,365,854)	(674)	2,379
Issuance of common stock pursuant to equity award plans (in shares)		480
Issuance of common stock pursuant to equity award plans	6,413		6,413
Stock-based compensation expense	11,394		11,394
Other comprehensive income (loss)	237				237
Net (loss) income	(71,177)			(71,303)		126
Balance at end of the year (in shares) at Sep. 30, 2018		66,434
Balance at end of the year at Sep. 30, 2018	166,928	$ 67	1,601,950	(1,437,157)	(437)	2,505
Balance at beginning of year (in shares) at Dec. 31, 2018		66,618
Balance at beginning of year at Dec. 31, 2018	90,567	$ 68	1,614,320	(1,525,704)	(283)	2,166
Issuance of common stock pursuant to equity award plans (in shares)		1,359
Issuance of common stock pursuant to equity award plans	25,662	$ 2	25,660
Stock-based compensation expense	12,312		12,312
Other comprehensive income (loss)	203				203
Net (loss) income	(78,096)			(78,156)		60
Change in noncontrolling interest	2					2
Balance at end of the year (in shares) at Mar. 31, 2019		67,977
Balance at end of the year at Mar. 31, 2019	50,650	$ 70	1,652,292	(1,603,860)	(80)	2,228
Balance at beginning of year (in shares) at Dec. 31, 2018		66,618
Balance at beginning of year at Dec. 31, 2018	90,567	$ 68	1,614,320	(1,525,704)	(283)	2,166
Net (loss) income	(196,200)
Balance at end of the year (in shares) at Sep. 30, 2019		77,784
Balance at end of the year at Sep. 30, 2019	212,888	$ 79	1,932,428	(1,719,691)	72	0
Balance at beginning of year (in shares) at Mar. 31, 2019		67,977
Balance at beginning of year at Mar. 31, 2019	50,650	$ 70	1,652,292	(1,603,860)	(80)	2,228
Issuance of common stock pursuant to equity award plans (in shares)		258
Issuance of common stock pursuant to equity award plans	5,966		5,966
Stock-based compensation expense	12,369		12,369
Other comprehensive income (loss)	41				41
Net (loss) income	(68,477)			(66,204)		(2,273)
Change in noncontrolling interest	45					45
Balance at end of the year (in shares) at Jun. 30, 2019		68,235
Balance at end of the year at Jun. 30, 2019	594	$ 70	1,670,627	(1,670,064)	(39)	0
Issuance of common stock pursuant to equity award plans (in shares)		308
Issuance of common stock pursuant to equity award plans	6,479		6,479
Issuance of common stock pursuant to public offering, net (in shares)		9,241
Issuance of common stock pursuant to public offering, net	243,715	$ 9	243,706
Stock-based compensation expense	11,616		11,616
Other comprehensive income (loss)	111				111
Net (loss) income	(49,627)			(49,627)
Balance at end of the year (in shares) at Sep. 30, 2019		77,784
Balance at end of the year at Sep. 30, 2019	$ 212,888	$ 79	$ 1,932,428	$ (1,719,691)	$ 72	$ 0