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Summary of Significant Accounting Policies - Premises and Equipment (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Jan. 17, 2017	Dec. 31, 2016
Transfers and Servicing of Financial Assets
Mortgage loans serviced for others	$ 695,100,000		$ 668,200,000
Estimated stranded disproportionate tax expense,net	$ 318,000
Subsequent Events
Cash dividend declared (per share)		$ 0.01
Buildings | Minimum
Premises and equipment
Useful lives	25 years
Buildings | Maximum
Premises and equipment
Useful lives	40 years
Building improvements | Minimum
Premises and equipment
Useful lives	3 years
Building improvements | Maximum
Premises and equipment
Useful lives	15 years
Furniture and equipment | Minimum
Premises and equipment
Useful lives	3 years
Furniture and equipment | Maximum
Premises and equipment
Useful lives	10 years

X

- Definition

Fair value as of the balance sheet date of mortgage loans representing net future revenues from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

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Amount of the related income tax effect of a cumulative effect on retained earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22663-107794

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The per share amount of a dividend declared, but not paid, as of the financial reporting date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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