NET INCOME (LOSS) PER SHARE - Schedule of Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income (loss)	$ 116,666	$ 31,099	$ 10,618	$ 2,765	$ 709	$ (3,470)	$ (3,738)	$ (5,128)	$ 161,148	$ (11,627)	$ (45,192)
Notes due 2023 interest and financing costs, net									1,088	0	0
Adjusted net income (loss)									$ 162,236	$ (11,627)	$ (45,192)
Denominator:
Weighted average common shares outstanding (in shares)									116,713	99,619	82,939
Employee stock-based awards (in shares)									8,964	0	0
Warrants (in shares)									0	0	0
Weighted average common shares outstanding for diluted calculation (in shares)									131,644	99,619	82,939
Net income (loss) per share, basic (in USD per share)	$ 0.95	$ 0.25	$ 0.09	$ 0.03	$ 0.01	$ (0.03)	$ (0.04)	$ (0.06)	$ 1.38	$ (0.12)	$ (0.54)
Net income (loss) per share, diluted (in USD per share)	$ 0.88	$ 0.23	$ 0.08	$ 0.02	$ 0.01	$ (0.03)	$ (0.04)	$ (0.06)	$ 1.23	$ (0.12)	$ (0.54)
Convertible Notes | Convertible Senior Note Due 2024
Denominator:
Notes due (in shares)									451	0	0
Convertible Notes | Convertible Senior Notes Due 2023
Denominator:
Notes due (in shares)									5,516	0	0