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Mortgage Servicing Rights - Additional Information (Details) - USD ($) $ in Thousands | 12 Months Ended
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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

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- Definition 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. + References 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 + Details
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