SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 121,478	$ 118,567	$ 109,517	$ 96,675	$ 93,767	$ 89,912	$ 85,682	$ 83,225	$ 446,237	$ 352,586	$ 296,500
Gross profit	63,857	62,348	59,820	58,984	59,174	56,962	54,083	52,395
Loss from operations	(46,154)	(43,168)	(37,944)	(32,553)	(27,425)	(24,238)	(21,987)	(15,983)	(159,819)	(89,633)	(41,896)
Net income (loss)	$ (50,100)	$ (47,071)	$ (40,932)	$ (34,265)	$ (28,131)	$ (23,771)	$ (21,482)	$ (15,355)	$ (172,368)	$ (88,739)	$ (104,497)
Net income (loss) per share:
Basic and diluted (in dollars per share)	$ (0.49)	$ (0.47)	$ (0.42)	$ (0.36)	$ (0.29)	$ (0.25)	$ (0.23)	$ (0.16)	$ (1.72)	$ (0.94)	$ (1.14)