Loans and Loans Held for Sale - Restructured Loans for Periods Presented (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1]		$ 32,206	$ 11,384
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1]		25,159	269
Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1]		5,661	9,890
Residential mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1]		340	374
Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1]		1,037	847
Installment and other consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1],[2]		11	4
Performing TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			36,960	16,786
Performing TDRs | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans		$ 20,200	22,233	2,054
Performing TDRs | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			6,909	7,026
Performing TDRs | Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			1,425	1,912
Performing TDRs | Residential mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			2,013	2,214
Performing TDRs | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			4,371	3,568
Performing TDRs | Installment and other consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			9	12
Nonperforming TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			8,912	11,088
Nonperforming TDRs | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			6,713	1,139
Nonperforming TDRs | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			695	6,646
Nonperforming TDRs | Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			0	406
Nonperforming TDRs | Residential mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			822	1,543
Nonperforming TDRs | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			678	1,349
Nonperforming TDRs | Installment and other consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			4	5
Total TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			45,872	27,874
Total TDRs | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			28,946	3,193
Total TDRs | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			7,604	13,672
Total TDRs | Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			1,425	2,318
Total TDRs | Residential mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			2,835	3,757
Total TDRs | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			5,049	4,917
Total TDRs | Installment and other consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans			$ 13	$ 17

[1] Excludes loans that were fully paid off or fully charged-off by period end. The pre-modification balance represents the balance outstanding prior to modification. The post-modification balance represents the outstanding balance at period end.

[2] Consumer bankruptcy loans where the debt has been legally discharged through the bankruptcy court and not reaffirmed.