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Amount of current income tax expense (benefit) and deferred income tax expense (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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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority noncontrolling interest income (loss), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, increase (decrease) in enacted tax rate, prior year income taxes, increase (decrease) in deferred tax asset valuation allowance, and other adjustments.

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Income Taxes - Summary of Income Tax Reconciliation (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Federal income tax at expected statutory rate									$ 51,532	$ 62,629	$ 73,631
Tax-exempt interest, net of interest incurred to carry tax-exempt securities									(4,406)	(4,876)	(4,478)
Bank owned life insurance									(2,237)	(2,087)	(2,399)
State income tax expense, net of federal tax effect									12,866	9,904	8,204
Tax credits									(20,555)	(17,408)	(10,070)
Reduction in reserve for uncertainties									(6,971)	(1,821)	(1,105)
Other, net									833	638	2,965
Income tax expense	$ 7,827us-gaap_IncomeTaxExpenseBenefit	$ 10,654us-gaap_IncomeTaxExpenseBenefit	$ 11,751us-gaap_IncomeTaxExpenseBenefit	$ 830us-gaap_IncomeTaxExpenseBenefit	$ 16,061us-gaap_IncomeTaxExpenseBenefit	$ 7,143us-gaap_IncomeTaxExpenseBenefit	$ 10,961us-gaap_IncomeTaxExpenseBenefit	$ 12,814us-gaap_IncomeTaxExpenseBenefit	$ 31,062us-gaap_IncomeTaxExpenseBenefit	$ 46,979us-gaap_IncomeTaxExpenseBenefit	$ 66,748us-gaap_IncomeTaxExpenseBenefit