Loans and Loans Held for Sale - Summary of Restructured Loans (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Financing Receivable, Modifications [Line Items]
Restructured loans	[1]	$ 6,770	$ 438
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Restructured loans	[1]	6,041	0
Commercial construction
Financing Receivable, Modifications [Line Items]
Restructured loans	[1]	157	0
Home equity
Financing Receivable, Modifications [Line Items]
Restructured loans	[1]	555	438
Installment and other consumer
Financing Receivable, Modifications [Line Items]
Restructured loans		17	$ 0
Performing TDRs
Financing Receivable, Modifications [Line Items]
Restructured loans		20,035		$ 14,901
Performing TDRs | Commercial real estate
Financing Receivable, Modifications [Line Items]
Restructured loans		2,298		2,579
Performing TDRs | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Restructured loans		9,403		3,946
Performing TDRs | Commercial construction
Financing Receivable, Modifications [Line Items]
Restructured loans		2,400		2,420
Performing TDRs | Residential mortgage
Financing Receivable, Modifications [Line Items]
Restructured loans		2,178		2,039
Performing TDRs | Home equity
Financing Receivable, Modifications [Line Items]
Restructured loans		3,713		3,885
Performing TDRs | Installment and other consumer
Financing Receivable, Modifications [Line Items]
Restructured loans		43		32
Nonperforming TDRs
Financing Receivable, Modifications [Line Items]
Restructured loans		8,560		11,150
Nonperforming TDRs | Commercial real estate
Financing Receivable, Modifications [Line Items]
Restructured loans		944		967
Nonperforming TDRs | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Restructured loans		3,036		3,197
Nonperforming TDRs | Commercial construction
Financing Receivable, Modifications [Line Items]
Restructured loans		414		2,413
Nonperforming TDRs | Residential mortgage
Financing Receivable, Modifications [Line Items]
Restructured loans		2,640		3,585
Nonperforming TDRs | Home equity
Financing Receivable, Modifications [Line Items]
Restructured loans		1,520		979
Nonperforming TDRs | Installment and other consumer
Financing Receivable, Modifications [Line Items]
Restructured loans		6		9
Total TDRs
Financing Receivable, Modifications [Line Items]
Restructured loans		28,595		26,051
Total TDRs | Commercial real estate
Financing Receivable, Modifications [Line Items]
Restructured loans		3,242		3,546
Total TDRs | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Restructured loans		12,439		7,143
Total TDRs | Commercial construction
Financing Receivable, Modifications [Line Items]
Restructured loans		2,814		4,833
Total TDRs | Residential mortgage
Financing Receivable, Modifications [Line Items]
Restructured loans		4,818		5,624
Total TDRs | Home equity
Financing Receivable, Modifications [Line Items]
Restructured loans		5,233		4,864
Total TDRs | Installment and other consumer
Financing Receivable, Modifications [Line Items]
Restructured loans		$ 49		$ 41

[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.