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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1]	$ 25,800	$ 633	$ 36,712	$ 11,699
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1]	23,784	250	29,747	250
Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1]	1,527	0	5,860	10,348
Residential mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1]	0	186	160	380
Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1]	485	191	934	715
Installment and other consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans	[1]	4	$ 6	10	$ 6
Performing TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				38,434		$ 16,786
Performing TDRs | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans		$ 19,900		21,448		2,054
Performing TDRs | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				9,065		7,026
Performing TDRs | Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				1,913		1,912
Performing TDRs | Residential mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				1,922		2,214
Performing TDRs | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				4,076		3,568
Performing TDRs | Installment and other consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				10		12
Nonperforming TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				14,496		11,088
Nonperforming TDRs | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				10,880		1,139
Nonperforming TDRs | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				787		6,646
Nonperforming TDRs | Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				406		406
Nonperforming TDRs | Residential mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				1,195		1,543
Nonperforming TDRs | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				1,226		1,349
Nonperforming TDRs | Installment and other consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				2		5
Total TDRs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				52,930		27,874
Total TDRs | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				32,328		3,193
Total TDRs | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				9,852		13,672
Total TDRs | Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				2,319		2,318
Total TDRs | Residential mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				3,117		3,757
Total TDRs | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				5,302		4,917
Total TDRs | Installment and other consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured loans				$ 12		$ 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.