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Mortgage Servicing Rights - Schedule of Mortgage Servicing Rights (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Servicing Asset at Amortized Value, Balance [Roll Forward] |  |  |
Balance at end of year, net of valuation reserve | $ 24,770 | $ 18,457 |
Mortgage loans |  |  |
Servicing Asset at Amortized Value, Balance [Roll Forward] |  |  |
Servicing asset at amortized cost, before valuation reserve, beginning | 18,700 | 15,900 | $ 14,400
Acquisitions of mortgage servicing rights | 3,500 | 0 | 300
Originations of mortgage servicing rights | 5,600 | 5,800 | 3,600
Amortization expense | (3,000) | (3,000) | (2,400)
Servicing asset at amortized cost, before valuation reserve, ending | 24,800 | 18,700 | 15,900
Less valuation reserve | 0 | (200) | (200)
Balance at end of year, net of valuation reserve | 24,800 | 18,500 | 15,700
Principal balance of serviced loans underlying mortgage servicing rights | $ 3,636,700 | $ 3,127,500 | $ 2,906,200
Mortgage servicing rights as a percentage of serviced loans | 0.0068 | 0.0059 | 0.0054

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- Definition Servicing Asset As a Percentage of Serviced Loans Held-In-Portfolio + References No definition available. + Details
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- Definition Servicing Asset at Amortized Cost, Before Valuation Reserve + References No definition available. + Details
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- Definition This is the result of the principal amount outstanding of total loans managed or securitized less securitized loans and loans that are in the process of being securitized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719 + Details
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- Definition Amortized amount of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=7524895&loc=d3e120260-111741 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122492-111745 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 4 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122739-111746 + Details
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- Definition Amount of additions from purchases, assumption or transfer to contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 4 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122739-111746 + Details
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- Definition Amount of amortization of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 4 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122739-111746 + Details
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- Definition Reflects the estimated amount of impairment as of the balance sheet date of recognized servicing assets that are being amortized in proportion to and over the period of estimated net servicing income or loss. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 4 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122739-111746 + Details
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