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Retirement Plans (Schedule of Assets by Industry Type) (detail) - USD ($) $ in Thousands | Mar. 31, 2017 | Mar. 31, 2016 | Mar. 31, 2015
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | $ 207,829 | $ 176,238 | $ 157,948
MoneyMarketFundsMember |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | 1,585 | 1,497 |
Equity Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | 206,244 | 174,741 |
Equity Securities [Member] | Materials |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | 10,952 | 9,379 |
Equity Securities [Member] | Industrials |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | 25,383 | 30,355 |
Equity Securities [Member] | Telecommunication services |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | 18,060 | 9,325 |
Equity Securities [Member] | Consumer staples |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | 43,641 | 33,048 |
Equity Securities [Member] | Energy |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | 16,110 | 14,658 |
Equity Securities [Member] | Financials |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | 33,818 | 34,891 |
Equity Securities [Member] | Health Care |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | 17,587 | 10,538 |
Equity Securities [Member] | Information technology |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | 13,887 | 9,681 |
Equity Securities [Member] | Uitlities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets at beginning of year | $ 26,806 | $ 22,866 |

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