Loans and Loans Held for Sale - Summary of Restructured Loans (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Financing Receivable, Modifications [Line Items]
Restructured loans	[1]	$ 5,499	$ 6,770
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Restructured loans	[1]	5,201	6,041
Commercial construction
Financing Receivable, Modifications [Line Items]
Restructured loans	[1]	0	157
Residential mortgage
Financing Receivable, Modifications [Line Items]
Restructured loans	[1]	49	0
Home equity
Financing Receivable, Modifications [Line Items]
Restructured loans	[1]	249	555
Installment and other consumer
Financing Receivable, Modifications [Line Items]
Restructured loans	[1]	0	$ 17
Performing TDRs
Financing Receivable, Modifications [Line Items]
Restructured loans		23,002		$ 16,786
Performing TDRs | Commercial real estate
Financing Receivable, Modifications [Line Items]
Restructured loans		2,019		2,054
Performing TDRs | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Restructured loans		13,447		7,026
Performing TDRs | Commercial construction
Financing Receivable, Modifications [Line Items]
Restructured loans		1,913		1,912
Performing TDRs | Residential mortgage
Financing Receivable, Modifications [Line Items]
Restructured loans		2,025		2,214
Performing TDRs | Home equity
Financing Receivable, Modifications [Line Items]
Restructured loans		3,590		3,568
Performing TDRs | Installment and other consumer
Financing Receivable, Modifications [Line Items]
Restructured loans		8		12
Nonperforming TDRs
Financing Receivable, Modifications [Line Items]
Restructured loans		7,873		11,088
Nonperforming TDRs | Commercial real estate
Financing Receivable, Modifications [Line Items]
Restructured loans		1,074		1,139
Nonperforming TDRs | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Restructured loans		3,463		6,646
Nonperforming TDRs | Commercial construction
Financing Receivable, Modifications [Line Items]
Restructured loans		406		406
Nonperforming TDRs | Residential mortgage
Financing Receivable, Modifications [Line Items]
Restructured loans		1,520		1,543
Nonperforming TDRs | Home equity
Financing Receivable, Modifications [Line Items]
Restructured loans		1,406		1,349
Nonperforming TDRs | Installment and other consumer
Financing Receivable, Modifications [Line Items]
Restructured loans		4		5
Total TDRs
Financing Receivable, Modifications [Line Items]
Restructured loans		30,875		27,874
Total TDRs | Commercial real estate
Financing Receivable, Modifications [Line Items]
Restructured loans		3,093		3,193
Total TDRs | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Restructured loans		16,910		13,672
Total TDRs | Commercial construction
Financing Receivable, Modifications [Line Items]
Restructured loans		2,319		2,318
Total TDRs | Residential mortgage
Financing Receivable, Modifications [Line Items]
Restructured loans		3,545		3,757
Total TDRs | Home equity
Financing Receivable, Modifications [Line Items]
Restructured loans		4,996		4,917
Total TDRs | Installment and other consumer
Financing Receivable, Modifications [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.