Fair Value - Quantitative Information about Level 3 Fair Value Measurements for Financial Instruments Measured at Fair Value on Non Recurring Basis (Details) - Fair Value, Measurements, Nonrecurring - Significant Unobservable Inputs $ in Thousands	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Commercial, industrial, and agricultural
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 540	$ 2,055
Commercial mortgages
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 1,166	$ 679
Measurement Input, Loss Severity | Commercial, industrial, and agricultural | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.39	0.20
Measurement Input, Loss Severity | Commercial, industrial, and agricultural | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.78	0.60
Measurement Input, Loss Severity | Commercial, industrial, and agricultural | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.63	0.34
Measurement Input, Loss Severity | Commercial mortgages
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.15
Measurement Input, Loss Severity | Commercial mortgages | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input		0.15
Measurement Input, Loss Severity | Commercial mortgages | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.90	0.39
Measurement Input, Loss Severity | Commercial mortgages | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.37	0.33