NET INCOME (LOSS) PER SHARE - Calculation of Basic and Diluted Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income (loss)	$ 375,446	$ (38,453)	$ (62,813)
Basic shares:
Weighted-average common shares outstanding (in shares)	425,728	406,313	380,921
Weighted-average unvested shares (in shares)	(729)	(582)	(1,577)
Weighted-average shares used to compute basic net income (loss) per share (in shares)	424,999	405,731	379,344
Diluted shares:
Stock options and restricted stock units (in shares)	30,602	0	0
Convertible senior notes (in shares)	0	0	0
Common stock warrants (in shares)	10,432	0	0
Employee stock purchase plan (in shares)	43	0	0
Weighted-average shares used to compute diluted net loss per share (in shares)	466,076	405,731	379,344
Net income (loss) per share:
Basic (in USD per share)	$ 0.88	$ (0.09)	$ (0.17)
Diluted (in USD per share)	$ 0.81	$ (0.09)	$ (0.17)