Purchased Loans - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($)
Financing Receivable, Allowance for Credit Loss [Line Items]
Restructured loans discontinued past due period	90 days
Allowance for loan losses attributable to restructured loans	$ 52,162,000	$ 49,026,000
Purchased
Financing Receivable, Allowance for Credit Loss [Line Items]
Nonperforming loans charged off past due period	90 days
Number of restructured loans | loan	2	8
Restructured loans discontinued past due period	90 days	90 days
Average recorded investment in impaired loans	$ 14,151,000	$ 9,396,000	$ 7,687,000
Interest income recognized on impaired loans			299,000
Interest income recognized on credit-deteriorated loans	80,000	119,000
Modifications, recorded investment	7,275,000	7,495,000	8,965,000
Modifications, subsequent default, recorded investment	101,000	5,000	$ 212,000
Remaining availability under commitments to lend additional funds on restructured loans	6,000	3,000
Purchased | Nonaccruing Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Outstanding balance of restructured loans	106,000	413,000
Purchased | Restructured Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Outstanding balance of restructured loans	1,667,000	1,868,000
Allowance for loan losses attributable to restructured loans	$ 17,000	$ 58,000