Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets
Securities available for sale, at fair value	$ 3,914,960	$ 3,933,360
Mortgage loans held for sale	207,845	213,357
Mortgage loans held for investment, at fair value option	2,779	2,792
Derivative instruments	265,589	100,781
Liabilities
Derivative instruments	12,141	10,606
Level 1
Assets
Securities available for sale, at fair value	0	0
Mortgage loans held for investment, at fair value option	0	0
Level 2
Assets
Securities available for sale, at fair value	3,914,960	3,933,360
Mortgage loans held for investment, at fair value option	0	0
Level 3
Assets
Securities available for sale, at fair value	0	0
Mortgage loans held for investment, at fair value option	2,779	2,792
Recurring
Assets
Securities available for sale, at fair value	3,914,960	3,933,360
Mortgage loans held for sale	207,845	213,357
Mortgage loans held for investment, at fair value option	2,779	2,792
Derivative instruments	283,525	104,151
Total	4,409,109	4,253,660
Liabilities
Derivative instruments	23,798	11,799
Total	23,798	11,799
Recurring \| Level 1
Assets
Securities available for sale, at fair value	0	0
Mortgage loans held for sale	0	0
Mortgage loans held for investment, at fair value option	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, at fair value	3,914,960	3,933,360
Mortgage loans held for sale	207,845	213,357
Mortgage loans held for investment, at fair value option	0	0
Derivative instruments	283,525	104,151
Total	4,406,330	4,250,868
Liabilities
Derivative instruments	23,798	11,799
Total	23,798	11,799
Recurring \| Level 3
Assets
Securities available for sale, at fair value	0	0
Mortgage loans held for sale	0	0
Mortgage loans held for investment, at fair value option	2,779	2,792
Derivative instruments	0	0
Total	2,779	2,792
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 security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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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Fair value of financial and nonfinancial obligations.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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