Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) segment	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
New Accounting Pronouncements or Change in Accounting Principle
Provision (reversal) for expected credit losses	$ (100)	$ 800	$ (1,300)	$ (800)
Guaranty liabilities	29,908		29,908		$ 28,551	$ 27,729
Allowance for doubtful accounts, period increase (decrease)	(100)	1,300	(1,800)	1,100
Allowance for doubtful accounts	17,700		17,700		19,500
Allowance for credit loss	9,400		9,400		$ 9,400
Revenues	633,375	585,844	$ 1,179,874	1,106,643
Number of operating segments | segment			1
Capital markets
New Accounting Pronouncements or Change in Accounting Principle
Revenues	$ 162,040	141,573	$ 292,806	256,774
Capital markets | Revision of Prior Period, Reclassification, Adjustment
New Accounting Pronouncements or Change in Accounting Principle
Revenues		141,600		256,800
Investment sales | Revision of Prior Period, Reclassification, Adjustment
New Accounting Pronouncements or Change in Accounting Principle
Revenues		(77,600)		(149,600)
Commercial origination, net of investment sales | Revision of Prior Period, Reclassification, Adjustment
New Accounting Pronouncements or Change in Accounting Principle
Revenues		$ (64,000)		$ (107,200)