REVENUE RECOGNITION - Adoption Impact of ASC 606 (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Apr. 01, 2018	Mar. 31, 2018
Current assets:
Deferred sales commission costs	$ 14,443		$ 14,443		$ 11,234	$ 0
Other current assets	13,166		13,166		11,765	10,040
Non-current assets:
Deferred sales commission costs, non-current	30,893		30,893		26,942	0
Stockholders' equity:
Accumulated deficit	(222,170)		(222,170)		(161,563)	(201,464)
Income Statement Related Disclosures [Abstract]
Total revenue	89,912	$ 75,575	258,819	$ 217,156
Sales and marketing	60,717	48,830	169,952	131,103
Loss from operations	(24,238)	(18,247)	(62,208)	(28,166)
Net loss	$ (23,771)	$ (88,520)	$ (60,608)	$ (91,235)
Net loss per share:
Basic and Diluted (in dollars per share)	$ (0.25)	$ (0.96)	$ (0.64)	$ (0.99)
Statement of Cash Flows [Abstract]
Net loss	$ (23,771)	$ (88,520)	$ (60,608)	$ (91,235)
Deferred sales commission costs			(7,234)	0
Other current and non-current assets			(2,565)	(2,315)
Net cash provided by operating activities			(6,673)	19,378
Service
Income Statement Related Disclosures [Abstract]
Total revenue	85,911	71,891	245,378	205,105
Product
Income Statement Related Disclosures [Abstract]
Total revenue	4,001	$ 3,684	13,441	$ 12,051
ASC 605
Current assets:
Deferred sales commission costs	0		0			0
Other current assets	10,023		10,023			10,040
Non-current assets:
Deferred sales commission costs, non-current	0		0			0
Stockholders' equity:
Accumulated deficit	(270,649)		(270,649)			$ (201,464)
Income Statement Related Disclosures [Abstract]
Total revenue	89,580		258,552
Sales and marketing	63,276		177,186
Loss from operations	(27,129)		(69,709)
Net loss	$ (26,662)		$ (68,109)
Net loss per share:
Basic and Diluted (in dollars per share)	$ (0.28)		$ (0.72)
Statement of Cash Flows [Abstract]
Net loss	$ (26,662)		$ (68,109)
Deferred sales commission costs			0
Other current and non-current assets			(2,298)
Net cash provided by operating activities			(6,673)
ASC 605 | Service
Income Statement Related Disclosures [Abstract]
Total revenue	86,245		246,030
ASC 605 | Product
Income Statement Related Disclosures [Abstract]
Total revenue	3,335		12,522
Adjustments | Accounting Standards Update 2014-09
Current assets:
Deferred sales commission costs	14,443		14,443		11,234
Other current assets	3,143		3,143		1,725
Non-current assets:
Deferred sales commission costs, non-current	30,893		30,893		26,942
Stockholders' equity:
Accumulated deficit	48,479		48,479		$ 39,901
Income Statement Related Disclosures [Abstract]
Total revenue	332		267
Sales and marketing	(2,559)		(7,234)
Loss from operations	2,891		7,501
Net loss	$ 2,891		$ 7,501
Net loss per share:
Basic and Diluted (in dollars per share)	$ 0.03		$ 0.08
Statement of Cash Flows [Abstract]
Net loss	$ 2,891		$ 7,501
Deferred sales commission costs			(7,234)
Other current and non-current assets			(267)
Net cash provided by operating activities			0
Adjustments | Accounting Standards Update 2014-09 | Service
Income Statement Related Disclosures [Abstract]
Total revenue	(334)		(652)
Adjustments | Accounting Standards Update 2014-09 | Product
Income Statement Related Disclosures [Abstract]
Total revenue	$ 666		$ 919