Schedule I - Parent Company Only Financial Statements - Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss) available to common stockholders	$ 153,488	$ 50,918	$ 66,816
Adjustments to reconcile net income to net cash used in operating activities:
Deferred tax (benefit) expense	(11,947)	(16,549)	(4,196)
Decrease (increase) in operating assets:
Receivables from related parties	8,377	5,465	(4,215)
Other assets	1,543	(20,074)	5,239
(Decrease) increase in operating liabilities:
Accounts payable, accrued and other liabilities	106,919	57,949	(17,420)
CASH FLOWS FROM INVESTING ACTIVITIES:
Net cash provided by (used in) investing activities	0	0	0
CASH FLOWS FROM FINANCING ACTIVITIES:
Dividends to stockholders	(15,098)	(60,440)	(192,442)
Repurchase of Class A common stock	(365,398)	(6)	(1,236)
Net increase (decrease) in cash and cash equivalents	(286,607)	212,568	219,387
Cash and cash equivalents, and Cash segregated under regulatory requirements at beginning of period	853,406	640,838	421,451
Cash and cash equivalents, and Cash segregated under regulatory requirements at end of period	566,799	853,406	640,838
Supplemental cash information:
Cash paid during the period for interest	66,450	69,572	51,776
Supplemental non-cash information:
Issuance of Class A common stock upon exchange of limited partnership interests	157,547	11,388	26,146
Issuance Of Class Common Stock And Limited Partnership Interests For Acquisitions	1,160	1,578	3,040
Parent Company
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss) available to common stockholders	124,007	45,062	43,901
Adjustments to reconcile net income to net cash used in operating activities:
Amortization of deferred financing costs	3,592	4,188	3,206
Equity (income) loss of subsidiaries	(114,971)	(38,030)	(46,752)
Deferred tax (benefit) expense	(6,404)	(13,585)	(20,042)
Decrease (increase) in operating assets:
Investments in subsidiaries	335,295	(11,480)	12,400
Receivables from related parties	(7,280)	1,241	16,029
Note receivable from related party	251,312	(187,069)	(366,496)
Other assets	1,769	887	861
(Decrease) increase in operating liabilities:
Accounts payable, accrued and other liabilities	(21,459)	14,295	(4,125)
Net cash provided by (used in) operating activities	565,861	(184,491)	(361,018)
CASH FLOWS FROM FINANCING ACTIVITIES:
Dividends to stockholders	(15,098)	(60,440)	(192,442)
Repurchase of Class A common stock	(365,398)	(5)	(970)
Issuance of senior notes, net of deferred issuance costs	0	294,396	294,845
Repayments of senior notes	(256,032)	(43,968)	0
Unsecured revolving credit agreement borrows	300,000	230,000	390,000
Unsecured revolving credit agreement repayments	(300,000)	(300,000)	(320,000)
Distributions from subsidiaries	70,602	61,972	184,545
Proceeds from issuance of Class A common stock, net of costs	72	2,516	4,929
Net cash provided by (used in) financing activities	(565,854)	184,471	360,907
Net increase (decrease) in cash and cash equivalents	7	(20)	(111)
Cash and cash equivalents, and Cash segregated under regulatory requirements at beginning of period	24	44	155
Cash and cash equivalents, and Cash segregated under regulatory requirements at end of period	31	24	44
Supplemental cash information:
Cash paid (refund) during the period for taxes	(157)	(5,919)	5,422
Cash paid during the period for interest	59,018	60,594	47,329
Supplemental non-cash information:
Issuance of Class A common stock upon exchange of limited partnership interests	157,547	11,388	26,146
Issuance Of Class Common Stock And Limited Partnership Interests For Acquisitions	$ 1,160	$ 1,578	$ 3,040