Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Effective Income Tax Rate Reconciliation [Line Items]
Tax at statutory rate, Amount	$ 19,814	$ 5,213	$ 8,126
Income from bank owned life insurance, Amount	(5,850)	(5,596)	(5,331)
Tax-exempt interest income, net, Amount	(2,789)	(3,453)	(5,688)
Tax credits, Amount	(267)	(270)	(304)
Other, Amount	(52)	89	(29)
Total tax provision (benefit), Amount	$ 14,658	$ (380)	$ 239
Tax at statutory rate, Pretax Income	35.00%	35.00%	35.00%
Income from bank owned life insurance, Pretax Income	(4.00%)	(13.00%)	(8.00%)
Tax-exempt interest income, net, Pretax Income	(5.00%)	(23.00%)	(25.00%)
Tax credits, Pretax Income	0.00%	(2.00%)	(1.00%)
Other, Pretax Income	0.00%	0.00%	0.00%
Total tax provision (benefit), Pretax Income	26.00%	(3.00%)	1.00%

Effective Income Tax Rate Reconciliation Bank Owned Life Insurance

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Earnings on or other increases in the value of the cash surrender value of bank owned life insurance policies.

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A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

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The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to all other items not otherwise listed in the existing taxonomy.

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The sum of the differences between the effective income tax rate and domestic federal statutory income tax rate that can be explained by all tax credits generated or utilized under enacted tax laws during the period.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to income that is exempt from income taxes under enacted tax laws.

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The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to continuing operations.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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The portion of the difference, between total income tax expense or benefit as reported in the Income Statement for the year/accounting period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations, that is attributable to all other items not otherwise listed in the existing taxonomy.

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The sum of the differences between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to tax credits.

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to income that is exempt from income taxes under enacted tax laws.

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