Loans and Allowance for Loan Losses - Schedule of Recorded Investment in Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Individually evaluated for impairment	$ 12,340	$ 14,341
Allowance for loan losses, Collectively evaluated for impairment	44,225	40,642
Allowance for loan losses, Loans acquired with deteriorated credit quality	345	478
Total allowance for loan losses	56,910	55,461
Loans and leases outstanding, Individually evaluated for impairment	113,897	118,514
Loans and leases outstanding, Collectively evaluated for impairment	11,865,874	12,080,985
Loans and leases outstanding, Loans acquired with deteriorated credit quality	37,877	44,393
Total loans and leases outstanding	12,017,648	12,243,892	$ 11,292,659
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Individually evaluated for impairment	7,855	6,035
Allowance for loan losses, Collectively evaluated for impairment	14,273	15,700
Allowance for loan losses, Loans acquired with deteriorated credit quality	1	7
Total allowance for loan losses	22,129	21,742
Loans and leases outstanding, Individually evaluated for impairment	40,270	35,410
Loans and leases outstanding, Collectively evaluated for impairment	2,904,851	3,191,367
Loans and leases outstanding, Loans acquired with deteriorated credit quality	5,438	6,193
Total loans and leases outstanding	2,950,559	3,232,970
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Individually evaluated for impairment	4,485	8,306
Allowance for loan losses, Collectively evaluated for impairment	19,621	14,845
Allowance for loan losses, Loans acquired with deteriorated credit quality	148	319
Total allowance for loan losses	24,254	23,470
Loans and leases outstanding, Individually evaluated for impairment	73,627	83,104
Loans and leases outstanding, Collectively evaluated for impairment	5,016,357	4,850,356
Loans and leases outstanding, Loans acquired with deteriorated credit quality	22,139	25,391
Total loans and leases outstanding	5,112,123	4,958,851
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Collectively evaluated for impairment	2,363	2,276
Allowance for loan losses, Loans acquired with deteriorated credit quality		1
Total allowance for loan losses	2,363	2,277
Loans and leases outstanding, Collectively evaluated for impairment	2,228,965	2,239,147
Loans and leases outstanding, Loans acquired with deteriorated credit quality	7,658	9,257
Total loans and leases outstanding	2,236,623	2,248,404
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Collectively evaluated for impairment	7,968	7,821
Allowance for loan losses, Loans acquired with deteriorated credit quality	196	151
Total allowance for loan losses	8,164	7,972
Loans and leases outstanding, Collectively evaluated for impairment	1,715,701	1,800,115
Loans and leases outstanding, Loans acquired with deteriorated credit quality	2,642	3,552
Total loans and leases outstanding	$ 1,718,343	$ 1,803,667

Reserve for loans impairments recorded after acquisition as a result of current information and events which result in it being probable that estimated cash flows will be less than previously expected or because actual cash flows are less than cash flows previously expected. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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