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Fair Value Measurements - Quantitative and Qualitative Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Quantitative information about Level 3 fair value measurements
Mortgage servicing rights, fair value	$ 7,541	$ 6,944
Minimum
Quantitative information about Level 3 fair value measurements
Discount rate (as a percent)		10.00%
Maximum
Quantitative information about Level 3 fair value measurements
Discount rate (as a percent)		34.30%
Weighted Average
Quantitative information about Level 3 fair value measurements
Discount rate (as a percent)		10.20%
Recurring | Mortgage servicing rights | Discounted Cash Flow | Level 3
Quantitative information about Level 3 fair value measurements
Mortgage servicing rights, fair value	$ 7,541
Recurring | Mortgage servicing rights | Discounted Cash Flow | Level 3 | Minimum
Quantitative information about Level 3 fair value measurements
Discount rate (as a percent)	10.00%
Prepayment speed (as a percent)	7.00%	7.00%
Recurring | Mortgage servicing rights | Discounted Cash Flow | Level 3 | Maximum
Quantitative information about Level 3 fair value measurements
Discount rate (as a percent)	106.30%
Prepayment speed (as a percent)	68.40%	68.40%
Recurring | Mortgage servicing rights | Discounted Cash Flow | Level 3 | Weighted Average
Quantitative information about Level 3 fair value measurements
Discount rate (as a percent)	10.20%
Prepayment speed (as a percent)	8.50%	9.60%

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+ References

No definition available.

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- Definition

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

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

+ 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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- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

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