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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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	$ 4,562	$ 25,800	$ 11,586	$ 36,712
Commercial real estate | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	171	23,784	2,381	29,747
Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	4,022	1,527	5,381	5,860
Commercial construction | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	0		2,561
Residential Mortgage | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	96	0	743	160
Home equity | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	269	485	515	935
Installment and other consumer | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	$ 4	$ 4	4	$ 10
Performing TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			18,478		$ 36,960
Performing TDRs | Commercial real estate | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			19		22,233
Performing TDRs | Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			7,322		6,909
Performing TDRs | Commercial construction | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			3,986		1,425
Performing TDRs | Business banking | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			1,539
Performing TDRs | Consumer real estate | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			5,606
Performing TDRs | Residential Mortgage | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans					2,013
Performing TDRs | Home equity | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans					4,371
Performing TDRs | Other consumer | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			6
Performing TDRs | Installment and other consumer | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans					9
Nonperforming TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			18,648		8,912
Nonperforming TDRs | Commercial real estate | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			14,504		6,713
Nonperforming TDRs | Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			1,549		695
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			441
Nonperforming TDRs | Consumer real estate | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			2,154
Nonperforming TDRs | Residential Mortgage | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans					822
Nonperforming TDRs | Home equity | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans					678
Nonperforming TDRs | Other consumer | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			0
Nonperforming TDRs | Installment and other consumer | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans					4
Total TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			37,126		45,872
Total TDRs | Commercial real estate | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			14,523		28,946
Total TDRs | Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			8,871		7,604
Total TDRs | Commercial construction | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			3,986		1,425
Total TDRs | Business banking | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			1,980
Total TDRs | Consumer real estate | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			7,760
Total TDRs | Residential Mortgage | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans					2,835
Total TDRs | Home equity | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans					5,049
Total TDRs | Other consumer | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			$ 6
Total TDRs | Installment and other consumer | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans					$ 13

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Amount, after troubled debt restructuring, of modified financing receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

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