Mortgage Servicing Rights - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Mortgage Loan Activity [Line Items]
Sale of 1-4 family mortgage loans	$ 93,991	$ 108,209	$ 99,458
Total servicing portfolio	441,000	407,000	361,000
Fannie Mae
Mortgage Loan Activity [Line Items]
Sale of 1-4 family mortgage loans	$ 78,800	$ 93,900	$ 76,800

The cash inflow from sales of loans that are secured with real estate mortgages and are held with the intention to resell in the near future.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 21
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3461-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration