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Fair Value Measurements - Loan Notes Issued by Variable Interest Entities (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016 | Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Gross written premiums | $ 822.1 | $ 801.7 | $ 1,820.1 | $ 1,777.4 |
Maximum | Level 3 |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Gross written premiums |  |  | 50.0 | 43.4 |
Reserve for losses |  |  | $ 7.4 | $ 11.8 |
Contract period |  |  | 365 days | 365 days |
Loan notes held by third parties | (325.0) |  | $ (325.0) |  | $ (220.0)
Minimum | Level 3 |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Gross written premiums |  |  | 42.9 | $ 38.9 |
Reserve for losses |  |  | 1.2 | 2.7 |
Loan notes held by third parties | (325.0) |  | (325.0) |  | (220.0)
Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Total | 7,555.4 |  | 7,555.4 |  | 7,653.6
Loan notes held by third parties | (110.8) |  | (110.8) |  | (115.0)
Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) | (4.7) |  | (4.7) |  | (108.4)
Fair Value, Measurements, Recurring | Level 3 |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Total | 115.5 |  | 115.5 |  | 223.4
Loan notes held by third parties | (110.8) |  | (110.8) |  | (115.0)
Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) | (4.7) | $ (1.4) | (4.7) | $ (1.4) | (108.4)
Fair Value, Measurements, Recurring | Level 3 | Silverton 2016 |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Total | $ 115.5 |  | $ 115.5 |  |
Fair Value, Measurements, Recurring | Level 3 | Silverton 2015 |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Total |  |  |  |  | $ 223.4

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- Definition Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 + Details
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- Definition This item represents the amount of the total realized and unrealized gains or losses for the period which are included in the statement of income (or changes in net assets); the fair value of which assets and liabilities was or is measured on a recurring basis using significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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