Income Taxes - Reconciliation of Income Tax (Details) - USD ($) $ in Thousands	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income tax expense computed at U.S. federal statutory rate	$ 121,681	$ 108,235	$ 135,667
Increases (reductions) resulting from:
State and local income taxes, net of federal tax	20,031	22,450	14,565
Foreign income taxes, net of federal tax	12,344	10,758	6,855
Meals and entertainment	1,761	1,771	2,247
Re-measurement of deferred taxes related to the 2017 Tax Act	0	(27,908)	(9,107)
Excess tax benefits from stock-based compensation	(10,265)	(10,777)	(14,457)
Research and development and other federal credits	(90,898)	(6,355)	(6,563)
Executive compensation -162(M)	2,346	2,615	345
IRS audit settlement	0	(2,573)	0
Foreign-Derived Intangible Income (FDII)	(4,915)	0	0
Changes in uncertain tax positions	44,621	(278)	140
Other	125	(1,064)	(1,348)
Total	$ 96,831	$ 96,874	$ 128,344
Federal statutory income tax rate	21.00%	21.00%	31.50%

Effective Income Tax Rate Reconciliation, Foreign Derived Intangible Income

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