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Changes in Fair Value of Loans Held for Sale (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Mortgage Banking Income | [1] | $ (19,177) | $ (33,069) | $ (6,082)
Loans held for sale |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Mortgage Banking Income | [1] | 899 | (5,616) | (472)
Mortgage servicing rights |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Mortgage Banking Income | [1] | $ (20,076) | $ (27,453) | $ (5,610)
[1] | Does not include the effect of hedging activities, which is included in "Other non-interest income."

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- Definition For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 30 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14172-108612 + Details
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