Prior Periods Financial Statement Revisions - Summary of Revision of Consolidated Statements of Financial Statements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accrued commissions and other receivables, net	$ 739,009				$ 788,284
Other assets	480,418				447,296
Total assets	3,949,300				3,926,914
Liabilities, Redeemable Partnership Interest, and Equity
Accounts payable, accrued and other liabilities	1,363,919				1,312,609
Total liabilities	3,120,397				3,178,308
Stockholders’ equity:
Additional paid-in capital	2,354,492				2,272,103
Retained deficit	(1,265,504)				(1,253,089)		$ (866,875)
Total stockholders’ equity	748,939				674,647
Noncontrolling interest in subsidiaries	59,290				50,321		501,208
Total equity	808,229	$ 767,681	$ 742,760	$ 696,324	724,968	$ 849,781		$ 1,127,870
Total liabilities, redeemable partnership interest, and equity	$ 3,949,300				3,926,914
As Reported [Member]
Assets
Accrued commissions and other receivables, net					778,415
Other assets					446,371
Total assets					3,916,120
Liabilities, Redeemable Partnership Interest, and Equity
Accounts payable, accrued and other liabilities					1,283,046
Total liabilities					3,148,745
Stockholders’ equity:
Additional paid-in capital					2,271,947
Retained deficit					(1,241,754)		(859,009)
Total stockholders’ equity					685,826
Noncontrolling interest in subsidiaries					57,911		505,855
Total equity		$ 802,625	$ 762,678	$ 715,956	743,737	863,174		1,139,741
Total liabilities, redeemable partnership interest, and equity					3,916,120
Adjustments [Member]
Assets
Accrued commissions and other receivables, net					9,869
Other assets					925
Total assets					10,794
Liabilities, Redeemable Partnership Interest, and Equity
Accounts payable, accrued and other liabilities					29,563
Total liabilities					29,563
Stockholders’ equity:
Additional paid-in capital					156
Retained deficit					(11,335)		(7,866)
Total stockholders’ equity					(11,179)
Noncontrolling interest in subsidiaries					(7,590)		$ (4,647)
Total equity					(18,769)	$ (13,393)		$ (11,871)
Total liabilities, redeemable partnership interest, and equity					$ 10,794