CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Mar. 31, 2019		134,602		(22,421)
Beginning 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	46,280				46,280
Change in cumulative foreign currency translation adjustment	(8,797)					(8,797)
Change in unrealized gains on cash flow hedge, net	1,276					1,276
Net unrealized gain on available-for-sale securities, net of taxes	722					722
Stock-based compensation	53,251		53,251
Repurchased common stock	0
Issuance of restricted stock, net of forfeitures and cancellations (in shares)		1,339
Issuance of restricted stock, net of forfeitures and cancellations	0	$ 13	(13)
Net share settlement of restricted stock awards (in shares)		(476)
Net share settlement of restricted stock awards	(52,118)	$ (5)	(52,113)
Employee share purchase plan settlement (in shares)		62
Employee share purchase plan settlement	5,133	$ 1	5,132
Ending balance (in shares) at Jun. 30, 2019		135,527		(22,421)
Ending balance at Jun. 30, 2019	2,086,327	$ 1,355	2,025,626	$ (820,572)	923,906	(43,988)
Beginning balance (in shares) at Mar. 31, 2020		135,927		(22,421)
Beginning balance at Mar. 31, 2020	2,539,244	$ 1,359	2,134,748	$ (820,572)	1,282,085	(58,376)
Increase (Decrease) in Stockholders' Equity
Net income	88,505				88,505
Change in cumulative foreign currency translation adjustment	4,701					4,701
Change in unrealized gains on cash flow hedge, net	(4,305)					(4,305)
Net unrealized gain on available-for-sale securities, net of taxes	5,849					5,849
Stock-based compensation	49,037		49,037
Issuance of restricted stock, net of forfeitures and cancellations (in shares)		979
Issuance of restricted stock, net of forfeitures and cancellations	0	$ 10	(10)
Net share settlement of restricted stock awards (in shares)		(282)
Net share settlement of restricted stock awards	(38,506)	$ (3)	(38,503)
Employee share purchase plan settlement (in shares)		65
Employee share purchase plan settlement	6,503	$ 1	6,502
Ending balance (in shares) at Jun. 30, 2020		136,689		(22,421)
Ending balance at Jun. 30, 2020	$ 2,651,028	$ 1,367	$ 2,151,774	$ (820,572)	$ 1,370,590	$ (52,131)