Allowance for Loan Losses - Schedule of Non Accrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	$ 16,287	$ 22,274
Mortgage Loans on Real Estate
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	9,513	14,309
Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	3,375	4,090
Commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	3,399	3,875
Residential 1-4 family | Mortgage Loans on Real Estate
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	3,728	3,578
Home equity loans | Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	1,668	1,769
Other | Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	93	7
Commercial loans | Mortgage Loans on Real Estate
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	5,785	10,731
Home equity lines of credit | Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	1,614	2,314
Originated
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	11,260	19,416
Originated | Mortgage Loans on Real Estate
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	5,352	12,507
Originated | Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	2,683	3,154
Originated | Commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	3,225	3,755
Originated | Residential 1-4 family | Mortgage Loans on Real Estate
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	2,820	3,244
Originated | Home equity loans | Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	1,405	1,722
Originated | Other | Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	90	3
Originated | Commercial loans | Mortgage Loans on Real Estate
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	2,532	9,263
Originated | Home equity lines of credit | Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	1,188	1,429
PNCI
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	5,027	2,858
PNCI | Mortgage Loans on Real Estate
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	4,161	1,802
PNCI | Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	692	936
PNCI | Commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	174	120
PNCI | Residential 1-4 family | Mortgage Loans on Real Estate
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	908	334
PNCI | Home equity loans | Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	263	47
PNCI | Other | Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	3	4
PNCI | Commercial loans | Mortgage Loans on Real Estate
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	3,253	1,468
PNCI | Home equity lines of credit | Consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	$ 426	$ 885