Benefit Plans (Restricted stock) (Details) - $ / shares	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Granted during the period (in dollars per share)			$ 101.61
Restricted Stock
Summary of the status and changes in restricted stock [Roll Forward]
Outstanding at beginning of period (in shares)	705,254
Granted during the period (in shares)	52,735	11,223	760,420
Vested during the period (in shares)	83,250
Forfeited during the period (in shares)	60,000
Outstanding at end of period (in shares)	614,739	705,254
Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding at beginning of period (in dollars per share)	$ 101.47
Granted during the period (in dollars per share)	106.28	$ 90.23
Vested during the period (in dollars per share)	101.17
Forfeited during the period (in dollars per share)	100.79
Outstanding at end of period (in dollars per share)	$ 101.99	$ 101.47

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Number of shares related to Restricted Stock Award forfeited during the period.

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Total number of shares issued during the period, including shares forfeited, as a result of Restricted Stock Awards.

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