Condensed Consolidated Statements of Stockholders’ Equity Condensed Consolidated Statements of Stockholders’ Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional paid-in capital [Member]	Accumulated other comprehensive income (loss) [Member]	Accumulated deficit [Member]
Beginning balance (in shares) at Dec. 31, 2017		238,756,522
Beginning balance at Dec. 31, 2017	$ 823,963	$ 24	$ 956,060	$ (9)	$ (132,112)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock	987		987
Issuance of common stock (in shares)		2,233,091
Stock-based compensation expense	24,148		24,148
Taxes related to net share settlement of restricted stock units	5,173		5,173
Net income (loss)	(80,877)				(80,877)
Other comprehensive income	338			338
Ending balance (in shares) at Mar. 31, 2018		240,989,613
Ending balance at Mar. 31, 2018	762,259	$ 24	976,022	329	(214,116)
Beginning balance (in shares) at Dec. 31, 2018		252,362,841
Beginning balance at Dec. 31, 2018	735,938	$ 25	1,055,046	(66)	(319,067)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock	931		931
Issuance of common stock (in shares)		2,381,188
Stock-based compensation expense	20,669		20,669
Taxes related to net share settlement of restricted stock units	6,422		6,422
Net income (loss)	(79,465)				(79,465)
Other comprehensive income	162			162
Ending balance (in shares) at Mar. 30, 2019		254,744,029
Ending balance at Mar. 30, 2019	$ 671,813	$ 25	$ 1,070,224	$ 96	$ (398,532)