Fair Value Measurement of Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring and Non-Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets
Equity securities	$ 41,410	$ 0
Available for sale securities	1,566,801	1,749,544
Liabilities
Foreclosed assets	9,400	9,500
Loans held for sale (which consist of residential mortgages) carried at fair value	74,500	34,600
U.S. Treasury securities
Assets
Available for sale securities	50,943	49,306
U.S. government agency securities
Assets
Available for sale securities	29,243	36,277
Obligations of states and political subdivisions
Assets
Available for sale securities	170,051	197,092
Residential mortgage-backed securities
Assets
Available for sale securities	1,254,786	1,429,782
Corporate and other debt securities
Assets
Available for sale securities	61,778	37,087
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements
Assets
Equity securities	41,410
Available for sale securities	50,943	49,306
Loans held for sale	0	0
Other assets	0	0
Total assets	92,353	49,306
Liabilities
Other liabilities	0	0
Total liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| U.S. Treasury securities
Assets
Available for sale securities	50,943	49,306
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| U.S. government agency securities
Assets
Available for sale securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Obligations of states and political subdivisions
Assets
Available for sale securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Residential mortgage-backed securities
Assets
Available for sale securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Corporate and other debt securities
Assets
Available for sale securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Non-recurring fair value measurements
Liabilities
Collateral dependent impaired loans	0	0
Loan servicing rights	0	0
Foreclosed assets	0	0
Total	0	0
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements
Assets
Equity securities	0
Available for sale securities	1,515,178	1,700,238
Loans held for sale	76,113	35,155
Other assets	158,532	48,979
Total assets	1,749,823	1,784,372
Liabilities
Other liabilities	43,926	23,681
Total liabilities	43,926	23,681
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| U.S. Treasury securities
Assets
Available for sale securities	0	0
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| U.S. government agency securities
Assets
Available for sale securities	29,243	36,277
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Obligations of states and political subdivisions
Assets
Available for sale securities	170,051	197,092
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Residential mortgage-backed securities
Assets
Available for sale securities	1,254,786	1,429,782
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Corporate and other debt securities
Assets
Available for sale securities	61,098	37,087
Significant Other Observable Inputs (Level 2) \| Non-recurring fair value measurements
Liabilities
Collateral dependent impaired loans	0	0
Loan servicing rights	0	0
Foreclosed assets	0	0
Total	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements
Assets
Equity securities	0
Available for sale securities	680	0
Loans held for sale	0	0
Other assets	0	0
Total assets	680	0
Liabilities
Other liabilities	0	0
Total liabilities	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| U.S. Treasury securities
Assets
Available for sale securities	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| U.S. government agency securities
Assets
Available for sale securities	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Obligations of states and political subdivisions
Assets
Available for sale securities	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Residential mortgage-backed securities
Assets
Available for sale securities	0	0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Corporate and other debt securities
Assets
Available for sale securities	680	0
Significant Unobservable Inputs (Level 3) \| Non-recurring fair value measurements
Liabilities
Collateral dependent impaired loans	39,075	45,245
Loan servicing rights	1,591	273
Foreclosed assets	10,807	5,673
Total	51,473	51,191
Fair Value \| Recurring fair value measurements
Assets
Equity securities	41,410
Available for sale securities	1,566,801	1,749,544
Loans held for sale	76,113	35,155
Other assets	158,532	48,979
Total assets	1,842,856	1,833,678
Liabilities
Other liabilities	43,926	23,681
Total liabilities	43,926	23,681
Fair Value \| Recurring fair value measurements \| U.S. Treasury securities
Assets
Available for sale securities	50,943	49,306
Fair Value \| Recurring fair value measurements \| U.S. government agency securities
Assets
Available for sale securities	29,243	36,277
Fair Value \| Recurring fair value measurements \| Obligations of states and political subdivisions
Assets
Available for sale securities	170,051	197,092
Fair Value \| Recurring fair value measurements \| Residential mortgage-backed securities
Assets
Available for sale securities	1,254,786	1,429,782
Fair Value \| Recurring fair value measurements \| Corporate and other debt securities
Assets
Available for sale securities	61,778	37,087
Fair Value \| Non-recurring fair value measurements
Liabilities
Collateral dependent impaired loans	39,075	45,245
Loan servicing rights	1,591	273
Foreclosed assets	10,807	5,673
Total	$ 51,473	$ 51,191

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

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Fair value of asset after deduction of liability.

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Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.

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Fair value of financial and nonfinancial obligations.

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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Fair value of the collateral dependent impaired loans.

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