Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Class A Common Stock	Common Stock Class A Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Balance (in shares) at Mar. 31, 2017			155,901,485	(7,013,777)
Beginning of year at Mar. 31, 2017	$ 584,873		$ 1,559	$ (191,900)	$ 302,907	$ 489,384	$ (17,077)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			866,099
Issuance of common stock	8,907		$ 8		8,899
Stock options exercised (in shares)			1,261,089
Stock options exercised	12,095		$ 13		12,082
Repurchase of common stock (in shares)				(7,568,357)
Repurchase of common stock	(269,557)			$ (269,557)
Recognition of liability related to future stock option exercises	(248)				(248)
Net income	301,692					301,692
Other comprehensive loss, net of tax	4,822						4,822
Dividends paid	(103,411)					(103,411)
Stock-based compensation expense	23,318				23,318
Balance (in shares) at Mar. 31, 2018			158,028,673	(14,582,134)
End of year at Mar. 31, 2018	562,491		$ 1,580	$ (461,457)	346,958	690,516	(15,106)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			876,187
Issuance of common stock	11,266		$ 9		11,257
Stock options exercised (in shares)			1,019,965
Stock options exercised	12,116		$ 10		12,106
Repurchase of common stock (in shares)		(5,100,000)		(5,314,838)
Repurchase of common stock	(249,993)			$ (249,993)
Net income	418,529					418,529
Other comprehensive loss, net of tax	3,916						3,916
Dividends paid	(114,234)					(114,234)
Stock-based compensation expense	31,275				31,275
Balance (in shares) at Mar. 31, 2019			159,924,825	(19,896,972)
End of year at Mar. 31, 2019	675,366		$ 1,599	$ (711,450)	401,596	994,811	(11,190)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			833,258
Issuance of common stock	14,987		$ 8		14,979
Stock options exercised (in shares)			575,890
Stock options exercised	8,925		$ 6		8,919
Repurchase of common stock (in shares)		(2,500,000)		(2,717,080)
Repurchase of common stock	(186,645)			$ (186,645)
Recognition of liability related to future restricted stock units vesting	(757)				(757)
Net income	482,603					482,603
Other comprehensive loss, net of tax	(34,811)						(34,811)
Dividends paid	(146,602)					(146,602)
Stock-based compensation expense	43,290				43,290
Balance (in shares) at Mar. 31, 2020			161,333,973	(22,614,052)
End of year at Mar. 31, 2020	$ 856,356		$ 1,613	$ (898,095)	$ 468,027	$ 1,330,812	$ (46,001)