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
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

Amount of accumulated pre-tax unrealized gain before deducting pre-tax unrealized losses on investments in available-for-sale securities impacting investments.

No definition available.

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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.

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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

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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

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