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Interest-Bearing Deposits - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Deposits [Abstract] |  |  |
Interest-bearing demand deposit, money market | $ 919.1 | $ 779.2 |
Certificates of deposit in denominations of $100 thousand or more | 210.4 | 145.4 |
Interest expense related to certificates of deposit $100 thousand or greater | $ 1.5 | $ 1.2 | $ 1.8

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- Definition Amount of interest-bearing domestic money market demand account deposit liabilities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.12) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition Interest expense incurred on time deposits, including certificates of deposits, of $100,000 or more in domestic offices. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.6) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
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- Definition Amount of time deposit liabilities, including certificates of deposit, in denominations of $100,000 or more. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Industry Guide -Number 3 -Section V -Paragraph D-E + Details
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