Fair Value Disclosures (Fair Value, Investments, Entities That Calculate Net Asset Value Per Share) (Details) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019
Other Investment Vehicles [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other investments, at fair value		$ 2,626	$ 2,891
U.S. Insurance JV [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded commitments	[1],[2]	817	817
U.S. Insurance JV [Member] | Other Investment Vehicles [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other investments, at fair value	[2]	2,017	2,223
SPAC Funds [Member] | Other Investment Vehicles [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other investments, at fair value	[3]	$ 609	$ 668

[1] Not applicable.

[2] The U.S. Insurance JV invests in debt issued by small and medium sized U.S. and Bermuda insurance and reinsurance companies.

[3] The SPAC Fund invests in equity interests of SPACs.