Acquisition (Narrative) (Details) - USD ($)						3 Months Ended		12 Months Ended
	Jun. 01, 2022	Dec. 16, 2021	Feb. 26, 2021	Feb. 16, 2021	Oct. 01, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Amortization of Intangible Assets								$ 16,200,000	$ 8,000,000	$ 13,000,000
Estimated intangible assets acquired						$ 70,263,000	$ 77,386,000	70,263,000	77,386,000
Goodwill						234,005,000	234,005,000	234,005,000	234,005,000	147,084,000
Contingent Consideration Payable						38,648,000	62,223,000	38,648,000	62,223,000
Common stock issuance upon acquisition								1,881,000	23,060,000	926,000
Trade name
Business Acquisition [Line Items]
Estimated intangible assets acquired						531,000	1,431,000	$ 531,000	1,431,000
Trade name | Minimum
Business Acquisition [Line Items]
Estimated average remaining useful lives								1 year
Trade name | Maximum
Business Acquisition [Line Items]
Estimated average remaining useful lives								3 years
Customer relationships
Business Acquisition [Line Items]
Estimated intangible assets acquired						53,920,000	57,634,000	$ 53,920,000	57,634,000
Customer relationships | Minimum
Business Acquisition [Line Items]
Estimated average remaining useful lives								4 years
Customer relationships | Maximum
Business Acquisition [Line Items]
Estimated average remaining useful lives								14 years
Backlog
Business Acquisition [Line Items]
Estimated intangible assets acquired						6,100,000	6,100,000	$ 6,100,000	6,100,000
Estimated average remaining useful lives								1 year
Non-compete agreements
Business Acquisition [Line Items]
Estimated intangible assets acquired						344,000	344,000	$ 344,000	344,000
Estimated average remaining useful lives								5 years
Kelvin Re Limited
Business Acquisition [Line Items]
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed								$ 1,600,000
Business Combination, Consideration Transferred	$ 221,000,000
Cash	92,589,000
Other assets	94,000
Accounts payable, accrued expenses and other liabilities	(1,711,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	$ 221,025,000
Cowen Insurance
Business Acquisition [Line Items]
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed								200,000
Business Combination, Consideration Transferred			$ 12,700,000
Payments to Acquire Businesses, Gross			12,500,000
Escrow			200,000
Business Combination, Bargain Purchase, Gain Recognized, Amount			5,200,000
Business Combination Bargain Purchase Gain Related Tax Expense			1,300,000
Intangible assets			$ 4,794,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			10 years
Amortization of Intangible Assets						$ 400,000	$ 400,000
Cash			$ 14,844,000
Fixed assets			30,000
Other assets			12,828,000
Accounts payable, accrued expenses and other liabilities			(16,099,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net			17,951,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net			12,735,000
Compensation payable			(17,000)
Cowen Insurance | License
Business Acquisition [Line Items]
Intangible assets			200,000
Cowen Insurance | Customer-Related Intangible Assets
Business Acquisition [Line Items]
Intangible assets			$ 4,600,000
Portico
Business Acquisition [Line Items]
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed								$ 4,200,000
Business Combination, Consideration Transferred		$ 112,000,000
Payments to Acquire Businesses, Gross		91,300,000
Escrow		4,400,000
Intangible assets		19,900,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life								3 years 7 days
Amortization of Intangible Assets								$ 9,500,000	$ 400,000
Estimated intangible assets acquired		19,900,000
Cash		5,089,000
Operating lease right-of-use assets		2,707,000
Fixed assets		8,000
Other assets		514,000
Operating lease liabilities		(2,707,000)
Accounts payable, accrued expenses and other liabilities		(401,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		25,110,000
Goodwill		86,921,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net		$ 112,031,000
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, High				$ 58,000,000
Business Combination, Consideration Transferred, Percentage of Transaction, Cash		75.00%
Business Combination, Consideration Transferred, Percentage of Transaction, Equity		25.00%
Common stock issuance upon acquisition		$ 586,061
Business acquisition, share price		$ 37.11
Portico | Time-based Award
Business Acquisition [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Economic Performance Hurdles		60.00%
Business Combination, Consideration Transferred, Payable		$ 6,000,000
Portico | Performance and Time-based Award
Business Acquisition [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Economic Performance Hurdles		40.00%
Business Combination, Consideration Transferred, Payable		$ 4,000,000
Portico | Level 3 | Fair Value, Measurements, Recurring
Business Acquisition [Line Items]
Contingent Consideration Payable		20,700,000
Portico | Minimum
Business Acquisition [Line Items]
Estimated average remaining useful lives								1 year
Business Combination, Contingent Consideration, Liability, Annual Amount		19,300,000
Portico | Maximum
Business Acquisition [Line Items]
Estimated average remaining useful lives								4 years
Business Combination, Consideration Transferred, Payable		10,000,000
Portico | Maximum | Time-based Award
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Annual, Payable		3,600,000
Portico | Trade name
Business Acquisition [Line Items]
Estimated intangible assets acquired		400,000
Estimated average remaining useful lives								1 year
Portico | Customer relationships
Business Acquisition [Line Items]
Estimated intangible assets acquired		13,400,000
Estimated average remaining useful lives								4 years
Portico | Backlog
Business Acquisition [Line Items]
Estimated intangible assets acquired		$ 6,100,000
Estimated average remaining useful lives								1 year
MHT Partners
Business Acquisition [Line Items]
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed										800,000
Business Combination, Consideration Transferred					$ 9,900,000
Payments to Acquire Businesses, Gross					5,700,000
Intangible assets					1,224,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life									4 years 2 months 1 day
Amortization of Intangible Assets								$ 300,000	$ 300,000	$ 100,000
Estimated intangible assets acquired					1,224,000
Operating lease right-of-use assets					1,120,000
Fixed assets					101,000
Other assets					43,000
Operating lease liabilities					(1,446,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net					509,000
Goodwill					9,356,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net					9,865,000
Contingent Consideration Payable					4,200,000
Compensation payable					(533,000)
MHT Partners | Minimum
Business Acquisition [Line Items]
Estimated average remaining useful lives								3 years
MHT Partners | Maximum
Business Acquisition [Line Items]
Estimated average remaining useful lives								5 years
MHT Partners | Trade name
Business Acquisition [Line Items]
Estimated intangible assets acquired					131,000
Estimated average remaining useful lives									3 years
MHT Partners | Customer relationships
Business Acquisition [Line Items]
Estimated intangible assets acquired					749,000
Estimated average remaining useful lives									4 years
MHT Partners | Non-compete agreements
Business Acquisition [Line Items]
Estimated intangible assets acquired					$ 344,000
Estimated average remaining useful lives									5 years