Stock-Based Compensation Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	May 31, 2015	May 31, 2007
Stock Options, Restricted Stock Awards and Stock Appreciation Rights
Share-based compensation expense	$ 15,716	$ 29,056	$ 27,411
Additional disclosure
Unrecognized compensation cost related to unvested stock options, restricted stock awards, deferred stock awards and restricted stock units	$ 18,629
Weighted average period for recognition of unrecognized compensation cost	1 year 4 months 20 days
Employee Stock Option
Number of Options to Purchase Common Shares
Outstanding at the beginning of the period (in shares)	145,726	247,344	569,661
Granted (in shares)	0	0	0
Exercised (in shares)	(31,830)	(101,618)	(322,317)
Outstanding at the end of the period (in shares)	113,896	145,726	247,344
Exercisable at the end of the period (in shares)	113,896
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 17.18	$ 14.24	$ 13.31
Exercised (in dollars per share)	14.69	10.02	12.60
Outstanding at the end of the period (in dollars per share)	17.87	$ 17.18	$ 14.24
Exercisable at the end of the period (in dollars per share)	$ 17.87
Weighted Average Remaining Life (in years)
Outstanding at the end of the period	2 years 3 days
Exercisable at the end of the period	2 years 3 days
Aggregate Intrinsic Value
Outstanding at the end of the period	$ 1,261
Exercisable at the end of the period	1,261
Additional disclosure
Aggregate intrinsic value of options exercised	888	$ 4,215	$ 7,816
Income tax (expense) benefits realized from the exercise of stock options	$ 1,024	$ 3,388	$ 1,481
Restricted Stock
Number of Restricted Stock Awards
Unvested at the beginning of the period (in shares)	14,019	75,627	217,560
Vested (in shares)	(14,019)	(57,822)	(126,843)
Forfeited (in shares)		(3,786)	(15,090)
Unvested at the end of the period (in shares)		14,019	75,627
Weighted Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share)	$ 47.17	$ 40.04	$ 35.55
Vested (in dollars per share)	$ 47.17	37.93	32.64
Forfeited (in dollars per share)		45.88	37.55
Unvested at the end of the period (in dollars per share)		$ 47.17	$ 40.04
Performance-based awards
Stock Options, Restricted Stock Awards and Stock Appreciation Rights
Number of shares granted not expected to vest	315,780
Share-based compensation expense	$ 0
Restricted Stock Units R S U
Number of Restricted Stock Awards
Unvested at the beginning of the period (in shares)	1,393,120	1,521,989	1,979,616
Awarded (in shares)	761,467	775,532	731,363
Vested (in shares)	(704,207)	(612,854)	(436,225)
Forfeited (in shares)	(100,216)	(291,547)	(752,765)
Unvested at the end of the period (in shares)	1,350,164	1,393,120	1,521,989
Weighted Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share)	$ 37.76	$ 29.18	$ 27.29
Awarded (in dollars per share)	41.38	46.27	35.99
Vested (in dollars per share)	37.87	30.11	39.14
Forfeited (in dollars per share)	43.82	31.66	25.06
Unvested at the end of the period (in dollars per share)	$ 39.30	$ 37.76	$ 29.18
Amended And Restated Stock Option Plan 2000
Stock Options, Restricted Stock Awards and Stock Appreciation Rights
Shares available for future grant (in shares)	0
Number of shares reserved for issuance	0
2015 Plan
Stock Options, Restricted Stock Awards and Stock Appreciation Rights
Number of shares reserved for issuance	945,643			3,000,000
2015 Plan | Stock options, restricted stock and restricted stock units
Stock Options, Restricted Stock Awards and Stock Appreciation Rights
Vesting period	4 years
2015 Plan | Performance-based awards
Stock Options, Restricted Stock Awards and Stock Appreciation Rights
Vesting period	3 years
Stock Option And Incentive Plan 2007
Stock Options, Restricted Stock Awards and Stock Appreciation Rights
Shares available for future grant (in shares)	0
Number of shares reserved for issuance					830,670
Percentage of increase in authorized shares on each April 1, beginning in 2008	2.90%