CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total		Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings/(Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	1.00% Convertible Notes due 2018	1.00% Convertible Notes due 2018 Common Stock	1.00% Convertible Notes due 2018 Additional Paid-in Capital
Balance (in shares) at Mar. 31, 2017			119,813		(17,192)
Balance at Mar. 31, 2017	$ 1,003,728		$ 1,198	$ 1,452,754	$ (303,388)	$ (99,694)	$ (47,142)
Increase (Decrease) in Stockholders' Equity
Net income	173,533	[1]				173,533
Change in cumulative foreign currency translation adjustment	43,379						43,379
Change in unrealized gains on cash flow hedge, net	(10,191)						(10,191)
Net unrealized gain on available-for-sale securities, net of taxes	(1,778)						(1,778)
Stock-based compensation	293,214			293,214
Issuance of restricted stock, net of forfeitures and cancellations (in shares)			2,151
Issuance of restricted stock, net of forfeitures and cancellations	0		$ 21	(21)
Repurchased common stock (in shares)					(1,513)
Repurchased common stock	(154,792)				$ (154,792)
Conversion of 1.00% Convertible Notes Due 2018 (in shares)									12,082
Conversion of 1.00% Convertible Notes Due 2018								$ 255,084	$ 121	$ 254,963
Net share settlement of restricted stock awards (in shares)			(1,303)
Net share settlement of restricted stock awards	(112,884)		$ (13)	(112,871)
Balance (in shares) at Mar. 31, 2018			132,743		(18,705)
Balance at Mar. 31, 2018	1,488,970		$ 1,327	1,888,039	$ (458,180)	73,516	(15,732)
Increase (Decrease) in Stockholders' Equity
Net income	333,837	[1]				333,837
Change in cumulative foreign currency translation adjustment	(33,456)						(33,456)
Change in cumulative foreign currency translation adjustment	(28,803)
Change in unrealized gains on cash flow hedge, net	4,906						4,906
Net unrealized gain on available-for-sale securities, net of taxes	2,440						2,440
Stock-based compensation	219,460			219,460
Issuance of restricted stock, net of forfeitures and cancellations (in shares)			2,345
Issuance of restricted stock, net of forfeitures and cancellations	0		$ 23	(23)
Repurchased common stock (in shares)					(3,716)
Repurchased common stock	(362,392)				$ (362,392)
Conversion of 1.00% Convertible Notes Due 2018 (in shares)									377
Conversion of 1.00% Convertible Notes Due 2018								$ 8,112	$ 4	$ 8,108
Net share settlement of restricted stock awards (in shares)			(920)
Net share settlement of restricted stock awards	(101,293)		$ (9)	(101,284)
Employee share purchase plan settlement (in shares)			57
Employee share purchase plan settlement	$ 5,070		$ 1	5,069
Balance (in shares) at Mar. 31, 2019	134,602		134,602		(22,421)
Balance at Mar. 31, 2019	$ 2,040,580		$ 1,346	2,019,369	$ (820,572)	877,626	(37,189)
Increase (Decrease) in Stockholders' Equity
Net income	404,459					404,459
Change in cumulative foreign currency translation adjustment	(27,445)						(27,445)
Change in cumulative foreign currency translation adjustment	(27,445)
Change in unrealized gains on cash flow hedge, net	9,590						9,590
Net unrealized gain on available-for-sale securities, net of taxes	(3,332)						(3,332)
Stock-based compensation	192,845			192,845
Issuance of restricted stock, net of forfeitures and cancellations (in shares)			1,970
Issuance of restricted stock, net of forfeitures and cancellations	0		$ 19	(19)
Net share settlement of restricted stock awards (in shares)			(771)
Net share settlement of restricted stock awards	(87,968)		$ (8)	(87,960)
Employee share purchase plan settlement (in shares)			126
Employee share purchase plan settlement	$ 10,515		$ 2	10,513
Balance (in shares) at Mar. 31, 2020	135,927		135,927		(22,421)
Balance at Mar. 31, 2020	$ 2,539,244		$ 1,359	$ 2,134,748	$ (820,572)	$ 1,282,085	$ (58,376)

[1] Prior period amounts have been adjusted retrospectively to reflect the adoption of ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. Refer to Note 1 for further discussion.