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	118,095				118,095
Change in cumulative foreign currency translation adjustment	(21,364)					(21,364)
Change in unrealized gains on cash flow hedge, net	3,371					3,371
Net unrealized gain on available-for-sale securities, net of taxes	720					720
Stock-based compensation	96,706		96,706
Issuance of restricted stock, net of forfeitures and cancellations (in shares)		1,503
Issuance of restricted stock, net of forfeitures and cancellations	0	$ 15	(15)
Net share settlement of restricted stock awards (in shares)		(551)
Net share settlement of restricted stock awards	(61,478)	$ (6)	(61,472)
Employee share purchase plan settlement (in shares)		62
Employee share purchase plan settlement	5,133	$ 1	5,132
Ending balance (in shares) at Sep. 30, 2019		135,616		(22,421)
Ending balance at Sep. 30, 2019	2,181,763	$ 1,356	2,059,720	$ (820,572)	995,721	(54,462)
Beginning balance (in shares) at Jun. 30, 2019		135,527		(22,421)
Beginning balance at Jun. 30, 2019	2,086,327	$ 1,355	2,025,626	$ (820,572)	923,906	(43,988)
Increase (Decrease) in Stockholders' Equity
Net income	71,815				71,815
Change in cumulative foreign currency translation adjustment	(12,567)					(12,567)
Change in unrealized gains on cash flow hedge, net	2,095					2,095
Net unrealized gain on available-for-sale securities, net of taxes	(2)					(2)
Stock-based compensation	43,455		43,455
Issuance of restricted stock, net of forfeitures and cancellations (in shares)		164
Issuance of restricted stock, net of forfeitures and cancellations	0	$ 2	(2)
Net share settlement of restricted stock awards (in shares)		(75)
Net share settlement of restricted stock awards	(9,360)	$ (1)	(9,359)
Employee share purchase plan settlement	0
Ending balance (in shares) at Sep. 30, 2019		135,616		(22,421)
Ending balance at Sep. 30, 2019	2,181,763	$ 1,356	2,059,720	$ (820,572)	995,721	(54,462)
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	187,826				187,826
Change in cumulative foreign currency translation adjustment	23,562					23,562
Change in unrealized gains on cash flow hedge, net	(4,305)					(4,305)
Net unrealized gain on available-for-sale securities, net of taxes	4,295					4,295
Stock-based compensation	94,712		94,712
Issuance of restricted stock, net of forfeitures and cancellations (in shares)		1,094
Issuance of restricted stock, net of forfeitures and cancellations	0	$ 11	(11)
Net share settlement of restricted stock awards (in shares)		(341)
Net share settlement of restricted stock awards	(48,202)	$ (4)	(48,198)
Employee share purchase plan settlement (in shares)		65
Employee share purchase plan settlement	6,503	$ 1	6,502
Issuance of shares related to Playdots, Inc. acquisition (in shares)		604
Issuance of shares related to Playdots, Inc. acquisition	97,647	$ 6	97,641
Ending balance (in shares) at Sep. 30, 2020		137,349		(22,421)
Ending balance at Sep. 30, 2020	2,901,282	$ 1,373	2,285,394	$ (820,572)	1,469,911	(34,824)
Beginning balance (in shares) at Jun. 30, 2020		136,689		(22,421)
Beginning balance at Jun. 30, 2020	2,651,028	$ 1,367	2,151,774	$ (820,572)	1,370,590	(52,131)
Increase (Decrease) in Stockholders' Equity
Net income	99,321				99,321
Change in cumulative foreign currency translation adjustment	18,861					18,861
Net unrealized gain on available-for-sale securities, net of taxes	(1,554)					(1,554)
Stock-based compensation	45,675		45,675
Issuance of restricted stock, net of forfeitures and cancellations (in shares)		115
Issuance of restricted stock, net of forfeitures and cancellations	0	$ 1	(1)
Net share settlement of restricted stock awards (in shares)		(59)
Net share settlement of restricted stock awards	(9,696)	$ (1)	(9,695)
Employee share purchase plan settlement	0
Issuance of shares related to Playdots, Inc. acquisition (in shares)		604
Issuance of shares related to Playdots, Inc. acquisition	97,647	$ 6	97,641
Ending balance (in shares) at Sep. 30, 2020		137,349		(22,421)
Ending balance at Sep. 30, 2020	$ 2,901,282	$ 1,373	$ 2,285,394	$ (820,572)	$ 1,469,911	$ (34,824)