Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Assets
Securities available for sale, at fair value	$ 2,800,286,000	$ 2,158,853,000
Mortgage loans held for sale	166,247,000	139,950,000
Derivative instruments	24,393,000	28,798,000
Liabilities
Derivative instruments	18,058,000	15,411,000
Available-for-Sale Securities
Liabilities
Fair value assets transferred from Level 1 to Level 2	0	14,400,000
Recurring
Assets
Securities available for sale, at fair value	2,800,286,000	2,158,853,000
Mortgage loans held for sale	166,247,000	139,950,000
Derivative instruments	30,486,000	32,903,000
Total, Assets	2,997,019,000	2,331,706,000
Liabilities
Derivative instruments	24,939,000	31,354,000
Total	24,939,000	31,354,000
Recurring \| Level 1
Assets
Securities available for sale, at fair value	0	0
Mortgage loans held for sale	0	0
Derivative instruments	0	0
Total, Assets	0	0
Liabilities
Derivative instruments	0	0
Total	0	0
Recurring \| Level 2
Assets
Securities available for sale, at fair value	2,800,286,000	2,158,853,000
Mortgage loans held for sale	166,247,000	139,950,000
Derivative instruments	30,486,000	32,903,000
Total, Assets	2,997,019,000	2,331,706,000
Liabilities
Derivative instruments	24,939,000	31,354,000
Total	24,939,000	31,354,000
Recurring \| Level 3
Assets
Securities available for sale, at fair value	0	0
Mortgage loans held for sale	0	0
Derivative instruments	0	0
Total, Assets	0	0
Liabilities
Derivative instruments	0	0
Total	$ 0	$ 0

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This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a recurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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No definition available.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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Fair value of financial and nonfinancial obligations.

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Fair value portion of mortgage loans held-for-sale.

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