Fair Value of Assets and Liabilities - Valuation Assumptions (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Loans measured for impairment \| Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	21.00%	14.00%
Interest rate lock commitments \| Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pull through rate	92.15%	93.05%
Minimum \| Loans measured for impairment \| Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	0.00%	32.00%
Minimum \| Other real estate owned \| Market Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Estimated capital costs to completed improvements		25.00%
Minimum \| Mortgage servicing rights \| Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	9.69%	9.42%
Constant prepayment rate	8.09%	8.94%
Maximum \| Loans measured for impairment \| Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	100.00%	40.00%
Maximum \| Other real estate owned \| Market Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Estimated capital costs to completed improvements		32.00%
Maximum \| Mortgage servicing rights \| Income Approach Valuation Technique
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	10.36%	10.05%
Constant prepayment rate	10.85%	11.34%

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Adjustment to the discount rate used to measure fair value for lack of ability to convert business interests into cash quickly.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

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Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

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