CONDENSED 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)
Balance (in shares) at Mar. 31, 2018		132,743
Balance, Treasury stock (in shares) at Mar. 31, 2018				(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	71,693				71,693
Change in cumulative foreign currency translation adjustment	(26,817)
Change in cumulative foreign currency translation adjustment	(31,470)					(31,470)
Change in unrealized gains on cash flow hedge, net	1,125					1,125
Net unrealized gain on available-for-sale securities, net of taxes	409					409
Stock-based compensation	55,523		55,523
Repurchased common stock (in shares)				(1,597)
Repurchased common stock	(153,500)			$ (153,500)
Issuance of restricted stock, net of forfeitures and cancellations (in shares)		1,438
Issuance of restricted stock, net of forfeitures and cancellations	0	$ 14	(14)
Conversion of 1.00% Convertible Notes Due 2018 (in shares)		137
Conversion of 1.00% Convertible Notes Due 2018	2,931	$ 2	2,929
Net share settlement of restricted stock awards (in shares)		(507)
Net share settlement of restricted stock awards	(58,402)	$ (5)	(58,397)
Balance (in shares) at Jun. 30, 2018		133,811
Balance, Treasury stock (in shares) at Jun. 30, 2018				(20,302)
Balance at Jun. 30, 2018	$ 1,852,205	$ 1,338	1,888,080	$ (611,680)	615,482	(41,015)
Balance (in shares) at Mar. 31, 2019		134,602
Balance, Treasury stock (in shares) at Mar. 31, 2019	(22,421)			(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	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
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
Balance (in shares) at Jun. 30, 2019		135,527
Balance, Treasury stock (in shares) at Jun. 30, 2019	(22,421)			(22,421)
Balance at Jun. 30, 2019	$ 2,086,327	$ 1,355	$ 2,025,626	$ (820,572)	$ 923,906	$ (43,988)