Condensed Consolidated Statements of Changes in Stockholders' (Deficit) Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2017	$ 25	$ 1,486,690	$ (786)	$ (1,469,543)	$ 16,386
Balance (in shares) at Dec. 31, 2017	25,173
Stock-based compensation		38,415			38,415
Issuance of common stock from public and private placement offerings, net of underwriting fees and issuance costs	$ 5	261,357			261,362
Issuance of common stock from public and private placement offerings, net of underwriting fees and issuance costs (in shares)	4,258
Value of stock options exercised		3,201			3,201
Net proceeds from exercise of stock options		3,201			3,201
Net proceeds from exercise of stock options (in shares)	223
Employee withholding taxes related to stock-based awards		(1,458)			(1,458)
Other comprehensive income			(860)		(860)
Net loss				(221,237)	(221,237)
Balance at Sep. 30, 2018	$ 30	1,788,205	(1,646)	(1,690,780)	95,809
Balance (in shares) at Sep. 30, 2018	29,654
Balance at Dec. 31, 2017	$ 25	1,486,690	(786)	(1,469,543)	$ 16,386
Balance (in shares) at Dec. 31, 2017	25,173
Net proceeds from exercise of stock options (in shares)					69
Balance at Sep. 30, 2019	$ 33	2,157,080	(1,070)	(2,025,308)	$ 130,735
Balance (in shares) at Sep. 30, 2019	32,733
Balance at Jun. 30, 2018	$ 29	1,774,955	(2,082)	(1,626,326)	146,576
Balance (in shares) at Jun. 30, 2018	29,565
Stock-based compensation		11,994			11,994
Value of stock options exercised	$ 1	2,715			2,716
Net proceeds from exercise of stock options	$ 1	2,715			2,716
Net proceeds from exercise of stock options (in shares)	89
Employee withholding taxes related to stock-based awards		(1,459)			(1,459)
Other comprehensive income			436		436
Net loss				(64,454)	(64,454)
Balance at Sep. 30, 2018	$ 30	1,788,205	(1,646)	(1,690,780)	95,809
Balance (in shares) at Sep. 30, 2018	29,654
Balance at Dec. 31, 2018	$ 30	1,800,144	(2,259)	(1,778,785)	19,130
Balance (in shares) at Dec. 31, 2018	29,694
Stock-based compensation		42,809			42,809
Recognition of debt discount on 2026 Convertible Notes		85,915			85,915
Issuance of common stock from public and private placement offerings, net of underwriting fees and issuance costs	$ 3	227,177			227,180
Issuance of common stock from public and private placement offerings, net of underwriting fees and issuance costs (in shares)	2,880
Value of stock options exercised		2,511			2,511
Net proceeds from exercise of stock options		2,511			2,511
Net proceeds from exercise of stock options (in shares)	159
Employee withholding taxes related to stock-based awards		(1,476)			(1,476)
Other comprehensive income			1,189		1,189
Net loss				(246,523)	(246,523)
Balance at Sep. 30, 2019	$ 33	2,157,080	(1,070)	(2,025,308)	130,735
Balance (in shares) at Sep. 30, 2019	32,733
Balance at Jun. 30, 2019	$ 33	2,116,481	(836)	(1,940,475)	175,203
Balance (in shares) at Jun. 30, 2019	32,696
Stock-based compensation		13,130			13,130
Recognition of debt discount on 2026 Convertible Notes		26,577			26,577
Value of stock options exercised		773			773
Net proceeds from exercise of stock options		773			773
Net proceeds from exercise of stock options (in shares)	37
Employee withholding taxes related to stock based awards		(119)			(119)
Other comprehensive income			(234)		(234)
Net loss				(84,833)	(84,833)
Balance at Sep. 30, 2019	$ 33	$ 2,157,080	$ (1,070)	$ (2,025,308)	$ 130,735
Balance (in shares) at Sep. 30, 2019	32,733