Allowance for Loan Losses - Schedule of Non Accrual Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	$ 14,662	$ 22,274
Mortgage Loans on Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	9,528	14,309
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	3,045	4,090
Residential 1-4 family | Mortgage Loans on Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	4,423	3,578
Home equity loans | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	1,212	1,769
Other | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	31	7
Commercial | Mortgage Loans on Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	5,105	10,731
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	2,089	3,875
Home equity lines of credit | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	1,802	2,314
Originated
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	10,751	19,416
Originated | Mortgage Loans on Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	6,249	12,507
Originated | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	2,464	3,154
Originated | Residential 1-4 family | Mortgage Loans on Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	3,547	3,244
Originated | Home equity loans | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	1,181	1,722
Originated | Other | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	29	3
Originated | Commercial | Mortgage Loans on Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	2,702	9,263
Originated | Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	2,038	3,755
Originated | Home equity lines of credit | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	1,254	1,429
PNCI
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	3,911	2,858
PNCI | Mortgage Loans on Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	3,279	1,802
PNCI | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	581	936
PNCI | Residential 1-4 family | Mortgage Loans on Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	876	334
PNCI | Home equity loans | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	31	47
PNCI | Other | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	2	4
PNCI | Commercial | Mortgage Loans on Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	2,403	1,468
PNCI | Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	51	120
PNCI | Home equity lines of credit | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	$ 548	$ 885