Acquisition (Narrative) (Details) - USD ($)						12 Months Ended
	Dec. 16, 2021	Feb. 26, 2021	Feb. 16, 2021	Oct. 01, 2020	Jan. 02, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Contingent Consideration Payable						$ 62,223,000	$ 37,953,000
Common stock issuance upon acquisition						23,060,000	926,000	$ 14,446,000
Amortization of Intangible Assets						$ 8,000,000	13,000,000	13,100,000
Business Combination, Bargain Purchase, Gain Recognized, Amount								$ 0
Portico
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Percentage of Transaction, Equity	25.00%
Business Combination, Consideration Transferred, Percentage of Transaction, Cash	75.00%
Business Combination, Consideration Transferred	$ 112,000,000
Payments to Acquire Businesses, Gross	91,300,000
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, High			$ 58,000,000
Escrow	4,400,000
Common stock issuance upon acquisition	$ 586,061
Business acquisition, share price	$ 37.11
Intangible assets	$ 19,900,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life						3 years 7 days
Amortization of Intangible Assets						$ 400,000
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed						4,200,000
Portico | Time-based Award
Business Acquisition [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Econmic 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, Econmic 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]
Business Combination, Contingent Consideration, Liability, Annual Amount	19,300,000
Portico | Maximum
Business Acquisition [Line Items]
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
Cowen Insurance
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		$ 12,700,000
Payments to Acquire Businesses, Gross		12,500,000
Escrow		200,000
Intangible assets		$ 4,794,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		10 years
Amortization of Intangible Assets						300,000
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed						200,000
Business Combination, Bargain Purchase, Gain Recognized, Amount		$ 5,200,000
Business Combination Bargain Purchase Gain Related Tax Expense		1,300,000
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
Quarton
Business Acquisition [Line Items]
Business Combination, Consideration Transferred					$ 103,000,000
Payments to Acquire Businesses, Gross					75,300,000
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, High					40,000,000
Business Combination, Contingent Consideration, Liability, Annual Amount					10,000,000
Intangible assets					22,200,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life								2 years 9 months 18 days
Amortization of Intangible Assets						2,600,000	$ 8,900,000	$ 8,900,000
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed								$ 1,200,000
Quarton | Level 3
Business Acquisition [Line Items]
Contingent Consideration Payable					$ 27,700,000
MHT Partners
Business Acquisition [Line Items]
Business Combination, Consideration Transferred				$ 9,900,000
Payments to Acquire Businesses, Gross				5,700,000
Contingent Consideration Payable				4,200,000
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	$ 100,000
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed							$ 800,000