Schedule I - Parent Company Only Financial Statements - Statements of Cash Flows (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss) available to common stockholders			$ 38,775	$ 58,867	$ 153,488
Adjustments to reconcile net income to net cash used in operating activities:
Deferred tax (benefit) expense			(60,556)	(14,628)	(11,947)
Decrease (increase) in operating assets:
Receivables from related parties			(1,380)	3,621	8,377
Other assets			19,803	(8,469)	1,543
(Decrease) increase in operating liabilities:
Accounts payable, accrued and other liabilities			(34,595)	(37,841)	106,919
CASH FLOWS FROM INVESTING ACTIVITIES:
Net cash provided by (used in) investing activities			(90,707)	(53,330)	121,133
CASH FLOWS FROM FINANCING ACTIVITIES:
Dividends to stockholders			(17,381)	(14,859)	(15,098)
Repurchase of Class A common stock			(114,580)	(103,888)	(365,398)
Redemption of equity awards			(117,867)	(76,219)	(110,565)
Net increase (decrease) in cash and cash equivalents			170,886	(64,789)	(286,607)
Cash and cash equivalents, and Cash segregated under regulatory requirements at beginning of period		$ 502,010	502,010	566,799	853,406
Cash and cash equivalents, and Cash segregated under regulatory requirements at end of period	$ 672,896		672,896	502,010	566,799
Supplemental cash information:
Cash paid during the period for interest			80,664	53,655	66,450
Supplemental non-cash information:
Issuance of Class A common stock upon exchange of limited partnership interests			45,868	34,889	157,547
Issuance Of Class Common Stock And Limited Partnership Interests For Acquisitions			7,275	2,710	1,160
Parent Company
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss) available to common stockholders	36,991	(726)		48,712	124,007
Adjustments to reconcile net income to net cash used in operating activities:
Amortization of deferred financing costs	774	1,461		2,801	3,592
Equity (income) loss of subsidiaries	(36,991)	726		(48,712)	(114,971)
Deferred tax (benefit) expense	(51,527)	0		(20,341)	(6,404)
Decrease (increase) in operating assets:
Investments in subsidiaries	207,931	(552)		55,706	335,295
Receivables from related parties	(12,744)	253		878	(7,280)
Notes receivable from related party	(1,124,589)	(348,040)		(2,801)	251,312
Other assets	(87,613)	3,836		(1,052)	1,769
(Decrease) increase in operating liabilities:
Accounts payable, accrued and other liabilities	20,191	3,568		(5,750)	(21,459)
Net cash provided by (used in) operating activities	(1,047,577)	(339,474)		29,441	565,861
CASH FLOWS FROM INVESTING ACTIVITIES:
Net cash provided by (used in) investing activities	0	0		0	0
CASH FLOWS FROM FINANCING ACTIVITIES:
Dividends to stockholders	(9,360)	(7,558)		(14,859)	(15,098)
Repurchase of Class A common stock	(66,778)	(46,481)		(103,888)	(365,398)
Issuance of senior notes, net of deferred issuance costs	884,781	346,579		0	0
Redemption of equity awards	(155)		(1,043)	0	0
Repayments of senior notes	0	0		0	(256,032)
Unsecured revolving credit agreement borrows	239,033	0		0	300,000
Unsecured revolving credit agreement repayments	0	0		0	(300,000)
Distributions from subsidiaries	0	47,861		89,234	70,602
Proceeds from dividend reinvestment plan	85	84		90	72
Net cash provided by (used in) financing activities	1,047,606	339,442		(29,423)	(565,854)
Net increase (decrease) in cash and cash equivalents	29	(32)		18	7
Cash and cash equivalents, and Cash segregated under regulatory requirements at beginning of period	17	49	49	31	24
Cash and cash equivalents, and Cash segregated under regulatory requirements at end of period	29	17	$ 29	49	31
Supplemental cash information:
Cash paid (refund) during the period for taxes	0	9,581		5,269	(157)
Cash paid during the period for interest	10,702	26,404		49,375	59,018
Supplemental non-cash information:
Issuance of Class A common stock upon exchange of limited partnership interests	0	45,868		34,889	157,547
Issuance Of Class Common Stock And Limited Partnership Interests For Acquisitions	$ 4,514	$ 2,761		$ 2,710	$ 1,160