Loans and Allowance for Loan Losses - Schedule of Recorded Investment in Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Individually evaluated for impairment	$ 14,341	$ 10,078
Allowance for loan losses, Collectively evaluated for impairment	40,642	40,137
Allowance for loan losses, Loans acquired with deteriorated credit quality	478	166
Total allowance for loan losses	55,461	50,381
Loans and leases outstanding, Individually evaluated for impairment	118,514	92,331
Loans and leases outstanding, Collectively evaluated for impairment	12,080,985	10,982,264
Loans and leases outstanding, Loans acquired with deteriorated credit quality	44,393	43,526
Total loans and leases outstanding	12,243,892	11,118,121
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Individually evaluated for impairment	6,035	3,424
Allowance for loan losses, Collectively evaluated for impairment	15,700	15,790
Allowance for loan losses, Loans acquired with deteriorated credit quality	7	32
Total allowance for loan losses	21,742	19,246
Loans and leases outstanding, Individually evaluated for impairment	35,410	26,270
Loans and leases outstanding, Collectively evaluated for impairment	3,191,367	2,685,847
Loans and leases outstanding, Loans acquired with deteriorated credit quality	6,193	5,152
Total loans and leases outstanding	3,232,970	2,717,269
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Individually evaluated for impairment	8,306	6,654
Allowance for loan losses, Collectively evaluated for impairment	14,845	14,782
Allowance for loan losses, Loans acquired with deteriorated credit quality	319
Total allowance for loan losses	23,470	21,436
Loans and leases outstanding, Individually evaluated for impairment	83,104	66,061
Loans and leases outstanding, Collectively evaluated for impairment	4,850,356	4,266,665
Loans and leases outstanding, Loans acquired with deteriorated credit quality	25,391	21,826
Total loans and leases outstanding	4,958,851	4,354,552
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Collectively evaluated for impairment	2,276	1,763
Allowance for loan losses, Loans acquired with deteriorated credit quality	1
Total allowance for loan losses	2,277	1,763
Loans and leases outstanding, Collectively evaluated for impairment	2,239,147	2,155,750
Loans and leases outstanding, Loans acquired with deteriorated credit quality	9,257	11,303
Total loans and leases outstanding	2,248,404	2,167,053
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Collectively evaluated for impairment	7,821	7,802
Allowance for loan losses, Loans acquired with deteriorated credit quality	151	134
Total allowance for loan losses	7,972	7,936
Loans and leases outstanding, Collectively evaluated for impairment	1,800,115	1,874,002
Loans and leases outstanding, Loans acquired with deteriorated credit quality	3,552	5,245
Total loans and leases outstanding	$ 1,803,667	$ 1,879,247

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 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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