Condensed Consolidated Statements of Stockholders' Deficit - USD ($) $ in Thousands	Common Stock	Additional paid-in capital	Accumulated deficit	Total
Balance at Dec. 31, 2018	$ 154	$ 1,394,603	$ (1,591,128)	$ (196,371)
Balance (in shares) at Dec. 31, 2018	154,414,691
Increase (Decrease) in Stockholders' Equity
Issuance of common stock related to share-based awards and employee stock purchase plan	$ 2	3,486		3,488
Issuance of common stock related to share-based awards and employee stock purchase plan (in shares)	1,210,858
Share-based compensation expense related to share-based awards and employee stock purchase plan		14,988		14,988
Net income (loss)			(59,284)	(59,284)
Balance at Mar. 31, 2019	$ 156	1,413,077	(1,650,412)	(237,179)
Balance (in shares) at Mar. 31, 2019	155,625,549
Balance at Dec. 31, 2018	$ 154	1,394,603	(1,591,128)	(196,371)
Balance (in shares) at Dec. 31, 2018	154,414,691
Increase (Decrease) in Stockholders' Equity
Net income (loss)				(47,001)
Balance at Jun. 30, 2019	$ 156	1,421,215	(1,640,738)	(219,367)
Balance (in shares) at Jun. 30, 2019	156,442,332
Balance at Mar. 31, 2019	$ 156	1,413,077	(1,650,412)	(237,179)
Balance (in shares) at Mar. 31, 2019	155,625,549
Increase (Decrease) in Stockholders' Equity
Issuance of common stock related to share-based awards and employee stock purchase plan		1,801		1,801
Issuance of common stock related to share-based awards and employee stock purchase plan (in shares)	621,588
Share-based compensation expense related to share-based awards and employee stock purchase plan		6,337		6,337
Share-based compensation expense related to share-based awards and employee stock purchase plan (in shares)	195,195
Dividend of sGC business			(2,609)	(2,609)
Net income (loss)			12,283	12,283
Balance at Jun. 30, 2019	$ 156	1,421,215	(1,640,738)	(219,367)
Balance (in shares) at Jun. 30, 2019	156,442,332
Balance at Dec. 31, 2019	$ 158	1,478,823	(1,572,232)	$ (93,251)
Balance (in shares) at Dec. 31, 2019	157,535,962			157,535,962
Increase (Decrease) in Stockholders' Equity
Issuance of common stock related to share-based awards and employee stock purchase plan	$ 1	11,984		$ 11,985
Issuance of common stock related to share-based awards and employee stock purchase plan (in shares)	1,832,164
Share-based compensation expense related to share-based awards and employee stock purchase plan		6,364		6,364
Net income (loss)			3,345	3,345
Balance at Mar. 31, 2020	$ 159	1,497,171	(1,568,887)	(71,557)
Balance (in shares) at Mar. 31, 2020	159,368,126
Balance at Dec. 31, 2019	$ 158	1,478,823	(1,572,232)	$ (93,251)
Balance (in shares) at Dec. 31, 2019	157,535,962			157,535,962
Increase (Decrease) in Stockholders' Equity
Net income (loss)				$ 28,549
Balance at Jun. 30, 2020	$ 160	1,506,671	(1,543,683)	$ (36,852)
Balance (in shares) at Jun. 30, 2020	159,976,245			159,976,245
Balance at Mar. 31, 2020	$ 159	1,497,171	(1,568,887)	$ (71,557)
Balance (in shares) at Mar. 31, 2020	159,368,126
Increase (Decrease) in Stockholders' Equity
Issuance of common stock related to share-based awards and employee stock purchase plan	$ 1	2,409		2,410
Issuance of common stock related to share-based awards and employee stock purchase plan (in shares)	608,119
Share-based compensation expense related to share-based awards and employee stock purchase plan		7,091		7,091
Net income (loss)			25,204	25,204
Balance at Jun. 30, 2020	$ 160	$ 1,506,671	$ (1,543,683)	$ (36,852)
Balance (in shares) at Jun. 30, 2020	159,976,245			159,976,245