Summary of Activity for Nonvested Restricted Shares (Detail) - Restricted Stock [Member] - $ / shares	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Nonvested at Beginning of Year	233,120	300,115	328,059
Number of Shares, Granted	179,377	118,292	121,836
Number of Shares, Vested	(136,280)	(169,347)	(147,790)
Number of Shares, Cancelled	(9,127)	(15,940)	(1,990)
Number of Shares, Nonvested at End of Year	267,090	233,120	300,115
Weighted Average Grant Date Fair Value, Nonvested at Beginning of Year	$ 75.35	$ 78.94	$ 72.52
Weighted Average Grant Date Fair Value, Granted	63.83	90.08	105.73
Weighted Average Grant Date Fair Value, Vested	78.89	92.98	75.94
Weighted Average Grant Date Fair Value, Cancelled	71.46	58.64	100.88
Weighted Average Grant Date Fair Value, Nonvested at End of Year	$ 62.56	$ 75.35	$ 78.94