CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Mar. 31, 2016		89,213,205
Beginning balance, amount at Mar. 31, 2016	$ 275,306	$ 89	$ 389,260	$ (4,184)	$ (109,859)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock plans less withholding taxes (in shares)		2,576,785
Issuance of common stock under stock plans, less withholding taxes	4,560	$ 3	4,557
Withholding taxes from stock plans (in shares)		(289,899)
Withholding taxes from stock plans	(3,004)	$ (1)	(3,003)
Stock-based compensation expense	21,462		21,462
Income tax benefit from stock-based compensation	486		486
Unrealized investment gain (loss)	70			70
Foreign currency translation adjustment	(5,528)			(5,528)
Net loss	(4,751)				(4,751)
Ending balance (in shares) at Mar. 31, 2017		91,500,091
Ending balance, amount at Mar. 31, 2017	288,601	$ 91	412,762	(9,642)	(114,610)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock plans less withholding taxes (in shares)		2,709,990
Issuance of common stock under stock plans, less withholding taxes	2,182	$ 3	2,179
Repurchases of common stock (in shares)		(1,362,727)
Repurchases of common stock	(17,934)	$ (1)	(17,933)
Stock-based compensation expense	28,782		28,782
Income tax benefit from stock-based compensation	0
Unrealized investment gain (loss)	(259)			(259)
Foreign currency translation adjustment	4,256			4,256
Net loss	(104,497)				(104,497)
Ending balance (in shares) at Mar. 31, 2018		92,847,354
Ending balance, amount at Mar. 31, 2018	218,774	$ 93	425,790	(5,645)	(201,464)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock plans less withholding taxes (in shares)		3,272,534
Issuance of common stock under stock plans, less withholding taxes	4,486	$ 3	4,483
Stock-based compensation expense	45,548		45,548
Income tax benefit from stock-based compensation	0
Unrealized investment gain (loss)	473			473
Foreign currency translation adjustment	(2,181)			(2,181)
Equity component of convertible senior notes, net of issuance costs	31,128		31,128
Net loss	(88,739)				(88,739)
Ending balance (in shares) at Mar. 31, 2019		96,119,888
Ending balance, amount at Mar. 31, 2019	$ 249,390	$ 96	$ 506,949	$ (7,353)	$ (250,302)