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, 2018	Dec. 31, 2017
Assets
Available for sale	$ 1,749,544	$ 1,493,905
Liabilities
Foreclosed assets	9,500	9,800
Loans held for sale (which consist of residential mortgages) carried at fair value	34,600	14,800
U.S. Treasury securities
Assets
Available for sale	49,306	49,642
U.S. government agency securities
Assets
Available for sale	36,277	42,505
Obligations of states and political subdivisions
Assets
Available for sale	197,092	112,884
Residential mortgage-backed securities
Assets
Available for sale	1,429,782	1,223,295
Trust preferred securities
Assets
Available for sale		3,214
Corporate and other debt securities
Assets
Available for sale	37,087	51,164
Equity securities
Assets
Available for sale		11,201
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements
Assets
Available for sale	49,306
Available for sale		58,807
Loans held for sale	0	0
Other assets	0	0
Total assets	49,306	58,807
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	49,306
Available for sale		49,642
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| U.S. government agency securities
Assets
Available for sale	0
Available for sale		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	0
Available for sale		0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Residential mortgage-backed securities
Assets
Available for sale	0
Available for sale		0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Trust preferred securities
Assets
Available for sale		0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Corporate and other debt securities
Assets
Available for sale	0
Available for sale		7,783
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring fair value measurements \| Equity securities
Assets
Available for sale		1,382
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
Available for sale	1,700,238
Available for sale		1,427,738
Loans held for sale	35,155	15,119
Other assets	48,979	26,417
Total assets	1,784,372	1,469,274
Liabilities
Other liabilities	23,681	24,330
Total liabilities	23,681	24,330
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| U.S. Treasury securities
Assets
Available for sale	0
Available for sale		0
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| U.S. government agency securities
Assets
Available for sale	36,277
Available for sale		42,505
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Obligations of states and political subdivisions
Assets
Available for sale	197,092
Available for sale		112,884
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Residential mortgage-backed securities
Assets
Available for sale	1,429,782
Available for sale		1,215,935
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Trust preferred securities
Assets
Available for sale		3,214
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Corporate and other debt securities
Assets
Available for sale	37,087
Available for sale		43,381
Significant Other Observable Inputs (Level 2) \| Recurring fair value measurements \| Equity securities
Assets
Available for sale		9,819
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
Available for sale	0
Available for sale		7,360
Loans held for sale	0	0
Other assets	0	0
Total assets	0	7,360
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	0
Available for sale		0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| U.S. government agency securities
Assets
Available for sale	0
Available for sale		0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Obligations of states and political subdivisions
Assets
Available for sale	0
Available for sale		0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Residential mortgage-backed securities
Assets
Available for sale	0
Available for sale		7,360
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Trust preferred securities
Assets
Available for sale		0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Corporate and other debt securities
Assets
Available for sale	0
Available for sale		0
Significant Unobservable Inputs (Level 3) \| Recurring fair value measurements \| Equity securities
Assets
Available for sale		0
Significant Unobservable Inputs (Level 3) \| Non-recurring fair value measurements
Liabilities
Collateral dependent impaired loans	45,245	48,373
Loan servicing rights	273	5,350
Foreclosed assets	5,673	3,472
Total	51,191	57,195
Fair Value \| Recurring fair value measurements
Assets
Available for sale	1,749,544
Available for sale		1,493,905
Loans held for sale	35,155	15,119
Other assets	48,979	26,417
Total assets	1,833,678	1,535,441
Liabilities
Other liabilities	23,681	24,330
Total liabilities	23,681	24,330
Fair Value \| Recurring fair value measurements \| U.S. Treasury securities
Assets
Available for sale	49,306
Available for sale		49,642
Fair Value \| Recurring fair value measurements \| U.S. government agency securities
Assets
Available for sale	36,277
Available for sale		42,505
Fair Value \| Recurring fair value measurements \| Obligations of states and political subdivisions
Assets
Available for sale	197,092
Available for sale		112,884
Fair Value \| Recurring fair value measurements \| Residential mortgage-backed securities
Assets
Available for sale	1,429,782
Available for sale		1,223,295
Fair Value \| Recurring fair value measurements \| Trust preferred securities
Assets
Available for sale		3,214
Fair Value \| Recurring fair value measurements \| Corporate and other debt securities
Assets
Available for sale	37,087
Available for sale		51,164
Fair Value \| Recurring fair value measurements \| Equity securities
Assets
Available for sale		11,201
Fair Value \| Non-recurring fair value measurements
Liabilities
Collateral dependent impaired loans	45,245	48,373
Loan servicing rights	273	5,350
Foreclosed assets	5,673	3,472
Total	$ 51,191	$ 57,195

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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 and equity securities categorized neither as held-to-maturity nor trading.

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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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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 the collateral dependent impaired loans.

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