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Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017 | Dec. 31, 2016
Derivative |  |  |  |
Aggregate Fair Value of all Derivative Instruments with Credit Risk-related Contingent Features in a Liability Position | $ 51.4 |  | $ 52.2 |
Notional Amount of Derivatives | 881.2 | $ 1,021.6 | 904.5 | $ 1,052.0
Approximate Amount of Net Deferred Gains on Derivative Instruments Expected to be Amortized During the Next Twelve Months | 65.1 |  |  |
Component of Derivative Gain (Loss) Excluded from the Assessment of Hedge Effectiveness | 0.0 | 0.0 |  |
Discontinued Hedge Accounting Due to Instrument No Longer Qualifying as Fair Value Hedge | 0.0 | 0.0 |  |
Cash Flow Hedging | Interest Rate Swaps and Forwards |  |  |  |
Derivative |  |  |  |
Notional Amount of Derivatives | 343.9 |  | 343.9 |
Credit Default Swaps | Credit Risk Contract |  |  |  |
Derivative |  |  |  |
Notional Amount of Derivatives | 0.0 | 70.0 | 70.0 | 70.0
Credit Default Swaps | Not Designated as Hedging Instrument | Credit Risk Contract |  |  |  |
Derivative |  |  |  |
Notional Amount of Derivatives |  |  | 70.0 |
Credit Exposure |  |  |  |
Derivative |  |  |  |
Fair Value, Concentration of Risk, Derivative Instruments, Assets | 0.1 |  |  |
Receive Variable/Pay Fixed | Interest Rate Swaps |  |  |  |
Derivative |  |  |  |
Notional Amount of Derivatives | 48.0 | 105.4 | 48.0 | 105.5
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments | 0.5 | 1.1 |  |
Receive Variable/Pay Fixed | Fair Value Hedging | Interest Rate Swaps |  |  |  |
Derivative |  |  |  |
Notional Amount of Derivatives | 48.0 |  | 48.0 |
Receive Fixed/Pay Variable | Interest Rate Swaps |  |  |  |
Derivative |  |  |  |
Notional Amount of Derivatives | 250.0 | 250.0 | 250.0 | 250.0
Receive Fixed/Pay Variable | Fair Value Hedging | Interest Rate Swaps |  |  |  |
Derivative |  |  |  |
Notional Amount of Derivatives | 250.0 |  | 250.0 |
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments | 2.4 | 0.5 |  |
Receive Fixed/Pay Fixed | Interest Rate Swaps |  |  |  |
Derivative |  |  |  |
Notional Amount of Derivatives | 556.4 | $ 596.2 | 536.5 | $ 616.5
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments | 0.3 |  |  |
Receive Fixed/Pay Fixed | Fair Value Hedging | Interest Rate Swaps |  |  |  |
Derivative |  |  |  |
Notional Amount of Derivatives | 19.9 |  |  |
Receive Fixed/Pay Fixed | Not Designated as Hedging Instrument | Interest Rate Swaps |  |  |  |
Derivative |  |  |  |
Notional Amount of Derivatives | $ 192.6 |  | $ 192.6 |

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994 + Details
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- Definition Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959 + Details
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- Definition This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 15 -Paragraph 83 -URI http://asc.fasb.org/extlink&oid=77898254&loc=d3e34841-113949 + Details
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- Definition Net gain (loss) relating to components of the gain (loss) on the fair value hedging instrument excluded from the assessment of fair value hedge effectiveness. Recognized in earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986 + Details
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- Definition Amount of net gain (loss) recognized in earnings when a hedged firm commitment no longer qualifies as a fair value hedge. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986 + Details
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