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Related Party Transactions Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019 | Dec. 31, 2019
Related Party Transaction [Line Items] |  |  |  |  |
Services and other revenues | $ 341,402 | $ 200,495 | $ 587,396 | $ 393,839 |
Gross premium volume | 2,373,192 | 2,247,147 | 4,696,016 | 4,502,189 |
Ceded premiums written | 916,797 | 941,509 | 1,593,143 | 1,719,458 |
Reinsurance recoverables | 5,472,349 |  | 5,472,349 |  | $ 5,432,712
Syndicate 2357 and certain other Nephila Reinsurers [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Gross premium volume | 122,900 | 141,200 | 213,400 | 234,200 |
Ceded premiums written | 122,900 | 141,200 | 213,400 | 234,200 |
Reinsurance recoverables | 236,700 |  | 236,700 |  | $ 238,800
Hagerty Group, LLC [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Gross premium volume | 154,000 | 128,600 | 254,900 | 212,900 |
Ceded premiums written | 72,800 | 62,000 | 120,600 | 102,200 |
Insurance-linked Securities Operations [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Services and other revenues | 54,600 | 50,200 | 107,700 | 103,600 |
Insurance-linked Securities Operations [Member] | Unconsolidated entities managed by Nephila and MCIM [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Services and other revenues | $ 46,000 | $ 47,300 | $ 89,900 | $ 100,100 |

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- Definition Amount, after valuation allowance, recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, policy benefits and policy reserves. Excludes premiums paid under reinsurance contracts. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=99404803&loc=d3e21412-158489 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=99404803&loc=d3e21409-158489 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=99397103&loc=d3e6824-158387 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 825 -Section 50 -Paragraph 1B -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99380617&loc=SL75241803-196195 + Details
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