Fair Value Measurements - Summary of Company's Investments and Securities Positions (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023
Schedule Of Available For Sale Securities [Line Items]
Investments, Amortized cost	$ 135,492	$ 134,903
Investments, Gross unrealized gains	897	673
Investments, Gross unrealized losses	(481)	(715)
Investments, Fair value	135,908	134,861
Liabilities, Fair Value Disclosure [Abstract]
Securities sold, not yet purchased gross unrealized gains	44
Securities sold, not yet purchased gross unrealized losses			$ 0
Securities sold, not yet purchased, at fair value	9,167
U.S. Treasuries [Member]
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost	99,877	99,236
Trading securities, Gross unrealized gains		446
Trading securities, Gross unrealized losses	(350)
Trading securities, Fair value	99,527	99,682
Investments, Fair value	99,527	99,682
Liabilities, Fair Value Disclosure [Abstract]
Securities sold, not yet purchased amortized cost	9,211
Securities sold, not yet purchased gross unrealized gains	44
Securities sold, not yet purchased gross unrealized losses	0
Securities sold, not yet purchased, at fair value	9,167
Mutual Funds Held In Rabbi Trust [Member]
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost	10,315	10,962
Trading securities, Gross unrealized gains	878	172
Trading securities, Gross unrealized losses	(10)	(649)
Trading securities, Fair value	11,183	10,485
Investments, Fair value	11,183	10,485
Corporate Debt [Member]
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost	25,300	24,705
Trading securities, Gross unrealized gains	19	55
Trading securities, Gross unrealized losses	(121)	(66)
Trading securities, Fair value	25,198	24,694
Investments, Fair value	$ 25,198	$ 24,694