Loans and Loans Held for Sale - Summary of Restructured Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	$ 689	$ 4,561	$ 8,513	$ 11,585
Commercial real estate | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	0	0	0	2,210
Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	341	4,022	5,968	5,284
Commercial construction | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	0	0	0	2,561
Business banking | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	0	171	1,500	268
Consumer real estate | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	348	364	1,045	1,258
Other consumer | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	$ 0	$ 4	0	$ 4
Total TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			27,815		$ 46,748
Total TDRs | Commercial real estate | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			15,345		16,668
Total TDRs | Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			1,762		16,975
Total TDRs | Commercial construction | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			0		3,267
Total TDRs | Business banking | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			3,139		1,933
Total TDRs | Consumer real estate | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			7,569		7,900
Total TDRs | Other consumer | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			0		5
Performing TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			13,782		17,460
Performing TDRs | Commercial real estate | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			4,252		14
Performing TDRs | Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			1,762		7,090
Performing TDRs | Commercial construction | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			0		3,267
Performing TDRs | Business banking | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			1,647		1,503
Performing TDRs | Consumer real estate | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			6,120		5,581
Performing TDRs | Other consumer | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			0		5
Nonperforming TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			14,033		29,289
Nonperforming TDRs | Commercial real estate | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			11,093		16,654
Nonperforming TDRs | Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			0		9,885
Nonperforming TDRs | Commercial construction | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			0		0
Nonperforming TDRs | Business banking | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			1,492		430
Nonperforming TDRs | Consumer real estate | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			1,448		2,319
Nonperforming TDRs | Other consumer | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			$ 0		$ 0