Fair Value of Assets and Liabilities - Valuation Assumptions (Details)	Sep. 30, 2018	Dec. 31, 2017
Discount rate | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input		0.14
Discount rate | Minimum | Income Approach Valuation Technique
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.25	0.32
Discount rate | Minimum | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.0987	0.0942
Discount rate | Maximum | Income Approach Valuation Technique
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.65	0.40
Discount rate | Maximum | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.1100	0.1005
Pull through rate | Income Approach Valuation Technique
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate lock commitment, measurement input	0.9353	0.9305
Estimated capital costs to complete improvements | Minimum | Market Approach Valuation Technique
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned, measurement input		0.25
Estimated capital costs to complete improvements | Maximum | Market Approach Valuation Technique
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned, measurement input		0.32
Constant prepayment rate | Minimum | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.0820	0.0894
Constant prepayment rate | Maximum | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.1034	0.1134