Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
Trading securities, at fair value	$ 8,432	$ 4,987
Available for sale debt securities	2,138,442	1,886,724
Mortgage servicing assets, carrying amount	1,038	1,332
Mortgage banking derivatives, carrying amount assets	6,436	1,761
Interest rate swap derivatives, carrying amount assets	831,891	273,068
Liabilities:
Mortgage banking derivatives, carrying amount liability	6,126	305
Interest rate swap derivatives, carrying amount liability	842,451	275,033
Mortgage Backed Securities [Member]
Assets:
Available for sale debt securities	1,787,846	1,767,242
Municipal Securities [Member]
Assets:
Available for sale debt securities	96,883	93,895
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Trading securities, at fair value	8,432	4,987
Available for sale debt securities	2,138,442	1,886,724
Fair Value Measurements on Recurring [Member] \| Carrying value [Member]
Assets:
Trading securities, at fair value	8,432	4,987
Loans held for sale	188,316	142,801
Mortgage servicing assets, carrying amount	1,038	1,332
Mortgage banking derivatives, carrying amount assets	6,436	1,761
Interest rate swap derivatives, carrying amount assets	831,891	273,068
Liabilities:
Mortgage banking derivatives, carrying amount liability	6,126	305
Interest rate swap derivatives, carrying amount liability	842,451	275,033
Fair Value Measurements on Recurring [Member] \| Carrying value [Member] \| Corporate Debt Securities [Member]
Assets:
Available for sale debt securities	5,757	5,657
Fair Value Measurements on Recurring [Member] \| Carrying value [Member] \| Obligations of U.S. Government Sponsored Entities and Agencies [Member]
Assets:
Available for sale debt securities	147,959	19,930
Fair Value Measurements on Recurring [Member] \| Carrying value [Member] \| Mortgage Backed Securities [Member]
Assets:
Available for sale debt securities	1,787,846	1,767,242
Fair Value Measurements on Recurring [Member] \| Carrying value [Member] \| Municipal Securities [Member]
Assets:
Available for sale debt securities	96,883	93,895
Fair Value Measurements on Recurring [Member] \| Carrying value [Member] \| U.S. Treasuries [Member]
Assets:
Available for sale debt securities	99,997
Fair Value Measurements on Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Assets:
Trading securities, at fair value	8,432	4,987
Loans held for sale	188,316	142,801
Mortgage servicing assets, carrying amount	1,038	1,332
Mortgage banking derivatives, carrying amount assets	57	14
Interest rate swap derivatives, carrying amount assets	831,891	273,068
Liabilities:
Mortgage banking derivatives, carrying amount liability	6,032	288
Interest rate swap derivatives, carrying amount liability	842,451	275,033
Fair Value Measurements on Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Corporate Debt Securities [Member]
Assets:
Available for sale debt securities	5,757	5,657
Fair Value Measurements on Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Obligations of U.S. Government Sponsored Entities and Agencies [Member]
Assets:
Available for sale debt securities	147,959	19,930
Fair Value Measurements on Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Mortgage Backed Securities [Member]
Assets:
Available for sale debt securities	1,787,846	1,767,242
Fair Value Measurements on Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Municipal Securities [Member]
Assets:
Available for sale debt securities	96,883	93,895
Fair Value Measurements on Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| U.S. Treasuries [Member]
Assets:
Available for sale debt securities	99,997
Fair Value Measurements on Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Assets:
Mortgage banking derivatives, carrying amount assets	6,379	1,747
Liabilities:
Mortgage banking derivatives, carrying amount liability	$ 94	$ 17

Interest rate derivative assets at fair value that are designated as hedging instruments.

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Interest rate derivative liabilities at fair value that are designated as hedging instruments.

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- Definition

Mortgage banking derivative carrying amount assets.

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Mortgage banking derivatives carrying amount liability.

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Mortgage servising assets, carrying value.

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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).

+ References

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-Publisher FASB
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Amount, after allowance for bad debt, of loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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-Publisher FASB
-Name Accounting Standards Codification
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