Acquisition (Preliminary Purchase Price Allocation) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Jun. 01, 2022	Dec. 31, 2021	Dec. 16, 2021	Feb. 26, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Goodwill	$ 234,005		$ 234,005			$ 147,084
Cowen Insurance
Business Acquisition [Line Items]
Cash					$ 14,844
Securities owned, at fair value					1,571
Fixed assets					30
Intangible assets					4,794
Other assets					12,828
Compensation payable					(17)
Accounts payable, accrued expenses and other liabilities					(16,099)
Total net identifiable assets acquired and liabilities assumed					17,951
Bargain purchase gain					(5,216)
Total estimated purchase price					$ 12,735
Kelvin Re Limited
Business Acquisition [Line Items]
Cash		$ 92,589
Cash collateral pledged		316,049
Premiums receivable from cedants		58,904
Claims recoverable from insurers		52,526
Insurance and reinsurance assets		111,430
Other assets		94
Accounts payable, accrued expenses and other liabilities		(1,711)
Premiums and other costs payable to reinsurers		(5,400)
Claims liabilities		(292,026)
Insurance and reinsurance liabilities		(297,426)
Total net identifiable assets acquired and liabilities assumed		$ 221,025
Portico
Business Acquisition [Line Items]
Cash				$ 5,089
Operating lease right-of-use assets				2,707
Fixed assets				8
Intangible assets				19,900
Other assets				514
Operating lease liabilities				(2,707)
Accounts payable, accrued expenses and other liabilities				(401)
Total net identifiable assets acquired and liabilities assumed				25,110
Goodwill				86,921
Total estimated purchase price				$ 112,031