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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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-Publisher FASB
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- Definition

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, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.

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Fair Value Disclosures - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	$ 5,109,631	$ 4,393,029	$ 4,107,069
Loans held-for-sale	65,405	83,969	42,034
U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value			10,113
Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,517,017	2,426,876	1,807,671
Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,108,594	1,472,280	1,679,980
Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	447,053	489,316	604,554
IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,645	4,618	296
Forward mortgage-backed securities trades	0	0	0
Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	2,806	0	0
Forward mortgage-backed securities trades			0	$ 1,560	$ 3,200
Fair Value, Measurements, Recurring [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	5,109,631	4,393,029	4,107,069
Loans held-for-sale	61,511	79,585	39,659
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value			10,113
Fair Value, Measurements, Recurring [Member] \| Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,517,017	2,426,876	1,807,671
Fair Value, Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,108,594	1,472,280	1,679,980
Fair Value, Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	447,053	489,316	604,554
Fair Value, Measurements, Recurring [Member] \| IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,645	4,618	296
Fair Value, Measurements, Recurring [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Forward mortgage-backed securities trades	2,806	(1,560)	(3,200)
Fair Value, Measurements, Recurring [Member] \| Corporate Bonds [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	32,490		220
Fair Value, Measurements, Recurring [Member] \| Other Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	4,477	4,557	4,531
Fair Value, Measurements, Recurring [Member] \| Level 1 Inputs [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	4,477	4,557	14,644
Fair Value, Measurements, Recurring [Member] \| Level 1 Inputs [Member] \| U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value			10,113
Fair Value, Measurements, Recurring [Member] \| Level 1 Inputs [Member] \| Other Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	4,477	4,557	4,531
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	5,105,154	4,388,472	4,092,425
Loans held-for-sale	61,511	79,585	39,659
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,517,017	2,426,876	1,807,671
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,108,594	1,472,280	1,679,980
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	447,053	489,316	604,554
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,645	4,618	296
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Forward mortgage-backed securities trades	2,806	$ (1,560)	(3,200)
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Corporate Bonds [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	$ 32,490		$ 220