Related Party Transactions Related Party Transactions	6 Months Ended
Related Party Transactions Related Party Transactions	Jun. 30, 2020
Related Party Transactions [Abstract]
Related Party Transactions Disclosure [Text Block]	Related Party Transactions The Company engages in certain related party transactions in the normal course of business at arm's length. Insurance-Linked Securities Within the Company's insurance-linked securities operations, the Company provides investment and insurance management services through MCIM and Nephila. See note 12 for details regarding operations conducted through MCIM. Nephila serves as the investment manager to several Bermuda, Ireland and U.S. based private funds (the Nephila Funds). To provide access for the Nephila Funds to the insurance, reinsurance and weather markets, Nephila also provides managing general agent services and acts as an insurance manager to certain Bermuda Class 3 and 3A reinsurance companies and Lloyd’s Syndicate 2357 (Syndicate 2357) (collectively, the Nephila Reinsurers). The Company receives management fees for investment and insurance management services provided through its insurance-linked securities operations based on the net asset value of the accounts managed, and, for certain funds, incentive fees based on the annual performance of the funds managed. Nephila also receives commissions from the Nephila Reinsurers, which are based on the direct written premiums of the insurance contracts placed. For the quarter and six months ended June 30, 2020, total revenues from the Company's insurance-linked securities operations were $54.6 million and $107.7 million, respectively, of which $46.0 million and $89.9 million, respectively, were attributed to unconsolidated entities managed by Nephila and MCIM. For the quarter and six months ended June 30, 2019, total revenues from the Company's insurance-linked securities operations were $50.2 million and $103.6 million, respectively, of which $47.3 million and $100.1 million, respectively, were attributed to unconsolidated entities managed by Nephila and MCIM. Other related party transactions with the Company's insurance-linked securities operations are described below. Within the Company’s program services business, the Company has a program with Nephila through which the Company writes insurance policies that are ceded to Syndicate 2357 and certain other Nephila Reinsurers. Through this arrangement, Nephila utilizes certain of the Company’s licensed insurance companies to write U.S. catastrophe exposed property risk that is then ceded to Nephila Reinsurers. Gross premiums written through the Company’s program with Nephila were $122.9 million and $213.4 million for the quarter and six months ended June 30, 2020, respectively, and $141.2 million and $234.2 million for the quarter and six months ended June 30, 2019, respectively, all of which were ceded to Nephila Reinsurers. As of June 30, 2020 and December 31, 2019, reinsurance recoverables on the consolidated balance sheets included $236.7 million and $238.8 million, respectively, due from Nephila Reinsurers. Under this program, the Company bears underwriting risk for annual aggregate agreement year losses in excess of a limit the Company believes is unlikely to be exceeded. To the extent losses under this program exceed the prescribed limit, the Company is obligated to pay such losses to the cedents without recourse to the Nephila Reinsurers. While the Company believes losses under this program are unlikely, those losses, if incurred, could be material to the Company’s consolidated results of operations and financial condition. The Company has also entered into other assumed and ceded reinsurance transactions with the Nephila Reinsurers in the normal course of business, which are not material to the Company's consolidated financial statements. The Hagerty Group, LLC In June 2019, the Company acquired a minority ownership interest in The Hagerty Group, LLC (Hagerty Group), a company that primarily operates as a managing general agent under the names Hagerty Insurance Agency and Hagerty Classic Marine Insurance Agency (collectively, Hagerty), which is accounted for under the equity method. Hagerty Group also includes Hagerty Re, a Bermuda Class 3 reinsurance company. Essentia Insurance Company (Essentia), one of the Company’s insurance subsidiaries, is the exclusive insurance underwriter for Hagerty in the U.S., and a portion of this insurance is ceded to Hagerty Re. For the quarter and six months ended June 30, 2020, gross written premiums attributable to Hagerty written on Essentia were $154.0 million and $254.9 million, respectively, of which $72.8 million and $120.6 million, respectively, were ceded to Hagerty Re. For the quarter and six months ended June 30, 2019, gross written premiums attributable to Hagerty written on Essentia were $128.6 million and $212.9 million, respectively, of which $62.0 million and $102.2 million, respectively, were ceded to Hagerty Re.