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Securities - Summary of Amortized Cost and Estimated Fair Values of Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2014 | Mar. 31, 2013
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Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | $ 569,323 |
Gross Unrealized Gains | 7,134 |
Gross Unrealized Losses | (708) |
Estimated Fair Value, Total | 575,749 |
U S Treasury and Other Federal Agencies [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 474,579 |
Gross Unrealized Gains | 1,452 |
Gross Unrealized Losses | (498) |
Estimated Fair Value, Total | 475,533 |
Mortgage-backed securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 29,228 |
Gross Unrealized Gains | 637 |
Gross Unrealized Losses | (1) |
Estimated Fair Value, Total | 29,864 | 17,974
States and political subdivisions [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 53,456 |
Gross Unrealized Gains | 1,583 |
Gross Unrealized Losses | (68) |
Estimated Fair Value, Total | 54,971 |
Other securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 12,060 |
Gross Unrealized Gains | 3,462 |
Gross Unrealized Losses | (141) |
Estimated Fair Value, Total | $ 15,381 |

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- Definition Amount of accumulated pre-tax unrealized gain before deducting pre-tax unrealized losses on investments in available-for-sale securities impacting investments. + References No definition available. + Details
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- Definition Amount of accumulated pre-tax unrealized loss before deducting pre-tax unrealized gain on investments in available-for-sale securities impacting investments. + References No definition available. + Details
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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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