Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets
Securities available for sale	$ 2,755,425	$ 2,800,286
Mortgage loans held for sale	192,545	166,247
Derivative instruments	40,037	24,393
Liabilities
Derivative instruments	39,540	18,058
Level 1
Assets
Derivative instruments	0	0
Liabilities
Derivative instruments	0	0
Level 2
Assets
Derivative instruments	48,594	30,486
Liabilities
Derivative instruments	48,772	24,939
Level 3
Assets
Derivative instruments	0	0
Liabilities
Derivative instruments	0	0
Recurring
Assets
Securities available for sale	2,755,425	2,800,286
Mortgage loans held for sale	192,545	166,247
Derivative instruments	48,594	30,486
Total	2,996,564	2,997,019
Liabilities
Derivative instruments	48,772	24,939
Total	48,772	24,939
Recurring \| Level 1
Assets
Securities available for sale	0	0
Mortgage loans held for sale	0	0
Derivative instruments	0	0
Total	0	0
Liabilities
Derivative instruments	0	0
Total	0	0
Recurring \| Level 2
Assets
Securities available for sale	2,755,425	2,800,286
Mortgage loans held for sale	192,545	166,247
Derivative instruments	48,594	30,486
Total	2,996,564	2,997,019
Liabilities
Derivative instruments	48,772	24,939
Total	48,772	24,939
Recurring \| Level 3
Assets
Securities available for sale	0	0
Mortgage loans held for sale	0	0
Derivative instruments	0	0
Total	0	0
Liabilities
Derivative instruments	0	0
Total	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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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, after the 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 not subject to a master netting arrangement and not elected to be offset.

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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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