CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Class A	Class B	Total stockholders' equity	Common Stock Class A	Common Stock Class B	Treasury Stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss)	Stock subscriptions receivable
Beginning balance (in shares) at Mar. 31, 2017					22,026,811	50,883,299	(6,900,000)
Beginning balance at Mar. 31, 2017				$ 726,617	$ 22	$ 51	$ (193,572)	$ 854,750	$ 87,407	$ (21,917)	$ (124)
Increase (Decrease) in Stockholders' Equity
Shares issued (in shares)						1,331,370
Shares issued				7,985		$ 1		7,984
Stock compensation vesting (note 14)				41,900				41,900
Dividends				(51,305)					(51,305)
Stock subscriptions receivable redeemed				124							124
Secondary offering (in shares)					7,750,000	(7,750,000)
Secondary offerings				93,500	$ 8	$ (8)		93,500
Retired shares upon settlement of forward purchase agreement (in shares)		(430,237)	(811,635)			(6,900,000)	6,900,000
Retired shares upon settlement of forward purchase agreement		$ (15,131)	$ (33,332)	0		$ (7)	$ 193,572	(193,565)
Shares subject to forward purchase agreement (in shares)						2,000,000	(2,000,000)
Shares subject to forward purchase agreement				(93,500)		$ 2	$ (93,500)	(2)
Conversion of Class B to Class A shares (in shares)					1,252,242	(1,252,242)
Conversion of Class B to Class A shares				0	$ 1	$ (1)
Shares issued to non-employee directors (note 14) (in shares)					5,589
Shares issued to non-employee directors (note 14)				0
Shares purchased and retired under repurchase program (in shares)					(430,237)
Shares purchased and retired under repurchase program				15,139				15,139
Other shares repurchased/forfeited (in shares)						(1,124,495)
Other shares repurchased/forfeited				(36,352)		$ (1)		(36,351)
Adjustment of noncontrolling interest to redeemable value				(1,261)					(1,261)
Net income	$ 172,283			172,283					172,283
Change in unrealized translation	7,961			7,961						7,961
Total comprehensive income				180,244					172,283	7,961
Ending balance (in shares) at Mar. 31, 2018					30,604,405	37,187,932	(2,000,000)
Ending balance at Mar. 31, 2018				852,813	$ 31	$ 37	$ (93,500)	753,077	207,124	(13,956)	$ 0
Increase (Decrease) in Stockholders' Equity
Shares issued (in shares)						1,208,074
Shares issued				9,258		$ 1		9,257
Stock compensation vesting (note 14)				47,575				47,575
Class B shares sold (in shares)					525,217	(525,217)
Class B shares sold				0
Dividends				(70,415)					(70,415)
Secondary offering (in shares)					3,000,000	(3,000,000)
Secondary offerings				0	$ 3	$ (3)		0
Retired shares upon settlement of forward purchase agreement (in shares)		(1,481,114)	(36,958)			(2,000,000)	2,000,000
Retired shares upon settlement of forward purchase agreement		$ (69,180)	$ (1,700)	0		$ (2)	$ 93,500	(93,498)
Conversion of Class B to Class A shares (in shares)					5,545,724	(5,545,724)
Conversion of Class B to Class A shares				0	$ 6	$ (6)
Shares issued to non-employee directors (note 14) (in shares)					6,570
Shares issued to non-employee directors (note 14)				187				187
Shares purchased and retired under repurchase program (in shares)					(784,114)
Shares purchased and retired under repurchase program				34,975	$ 1			34,974
Other shares repurchased/forfeited (in shares)					(697,000)	(127,331)
Other shares repurchased/forfeited				(36,535)	$ (1)			(36,534)
Net income	159,106			159,106					159,106
Change in unrealized translation	(16,338)			(16,338)						(16,338)
Total comprehensive income				142,768					159,106	(16,338)
Ending balance (in shares) at Mar. 31, 2019		38,200,802	27,197,734		38,200,802	27,197,734	0
Ending balance at Mar. 31, 2019	891,329			891,329	$ 38	$ 27	$ 0	645,090	276,468	(30,294)
Increase (Decrease) in Stockholders' Equity
Shares issued (in shares)						1,546,486
Shares issued				8,713		$ 1		8,712
Stock compensation vesting (note 14)				56,901				56,901
Class B shares sold (in shares)					6,287,412	(6,287,412)
Class B shares sold				0	$ 6	$ (6)
Dividends				(82,790)					(82,790)
Retired shares upon settlement of forward purchase agreement (in shares)		(671,187)	(654,994)
Retired shares upon settlement of forward purchase agreement		$ (29,621)	$ (31,451)
Conversion of Class B to Class A shares (in shares)					2,352,461	(2,352,461)
Conversion of Class B to Class A shares				0	$ 2	$ (2)
Shares issued to non-employee directors (note 14) (in shares)					9,145
Shares issued to non-employee directors (note 14)				369				369
Other shares repurchased/forfeited (in shares)					(671,187)	(759,070)
Other shares repurchased/forfeited				(61,119)		$ (1)		(61,118)
Net income	183,793			183,793					183,793
Change in unrealized translation	(12,814)			(12,814)						(12,814)
Total comprehensive income				170,979					183,793	(12,814)
Ending balance (in shares) at Mar. 31, 2020		46,178,633	19,345,277		46,178,633	19,345,277
Ending balance at Mar. 31, 2020	$ 984,382			$ 984,382	$ 46	$ 19		$ 649,954	$ 377,471	$ (43,108)