Executive Stock Plans And Stock-Based Compensation (Summary Of RSU, Restricted Stock, And PSA Activity) (Details) - $ / shares shares in Thousands	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2016
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	85,463	87,621	72,032
Vested, Shares	(74,518)	(99,549)	(60,751)
Forfeited, Shares	0	0	0
Unvested at end of year, Shares	335,936	324,991	336,919	325,638
Granted, Weighted- Average Grant Date Fair Value	$ 56.39	$ 64.53	$ 64.13
Vested, Weighted- Average Grant Date Fair Value	54.20	59.09	45.51
Forfeited, Weighted- Average Grant Date Fair Value	0	0	0
Unvested at end of year, Weighted- Average Grant Date Fair Value	$ 57.89	$ 57.12	$ 55.77	$ 52.01
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	0	0	0
Vested, Shares	0	(8,950)	0
Forfeited, Shares	0	0	0
Unvested at end of year, Shares	21,250	21,250	30,200	30,200
Granted, Weighted- Average Grant Date Fair Value	$ 0	$ 0	$ 0
Vested, Weighted- Average Grant Date Fair Value	0	44.25	0
Forfeited, Weighted- Average Grant Date Fair Value	0	0	0
Unvested at end of year, Weighted- Average Grant Date Fair Value	$ 41.58	$ 41.58	$ 42.37	$ 42.37
Performance Share Awards Psas [Member
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	60,728	54,800	39,100
Vested, Shares	(67,402)	(49,092)	(41,667)
Forfeited, Shares	0	(9,834)	(6,783)
Unvested at end of year, Shares	140,200	146,874	151,000	160,350
Granted, Weighted- Average Grant Date Fair Value	$ 50.16	$ 57.12	$ 60.37
Vested, Weighted- Average Grant Date Fair Value	49.17	45.06	46.41
Forfeited, Weighted- Average Grant Date Fair Value	0	45.55	46.41
Unvested at end of year, Weighted- Average Grant Date Fair Value	$ 55.73	$ 55.12	$ 50.50	$ 46.86

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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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 number of grants made 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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-Publisher FASB
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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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-Publisher FASB
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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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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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