Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Commissions	$ 658,320	$ 577,172	$ 1,326,919	$ 1,122,892
Principal transactions	84,988	80,360	176,906	166,103
Gains from mortgage banking activities/originations, net	41,878	73,547	80,792	118,808
Real estate management and other services	107,121	51,589	203,999	102,219
Servicing fees	32,333	26,840	61,259	51,672
Fees from related parties	6,271	6,018	12,861	12,956
Data, software and post-trade	15,370	13,322	30,469	26,409
Interest income	12,366	19,177	21,114	29,183
Other revenues	1,429	876	2,403	1,852
Total revenues	960,076	848,901	1,916,722	1,632,094
Expenses:
Compensation and employee benefits	524,030	482,353	1,058,841	942,984
Allocations of net income and grant of exchangeability to limited partnership units and FPUs	106,545	50,237	171,777	113,430
Total compensation and employee benefits	630,575	532,590	1,230,618	1,056,414
Occupancy and equipment	52,428	50,311	107,212	101,140
Fees to related parties	9,887	5,519	17,651	12,009
Professional and consulting fees	26,918	22,891	52,999	44,561
Communications	34,143	32,353	68,993	64,526
Selling and promotion	32,900	30,034	62,749	54,675
Commissions and floor brokerage	15,623	10,476	29,718	20,906
Interest expense	27,441	26,490	54,579	45,253
Other expenses	66,307	50,269	134,898	92,662
Total expenses	896,222	760,933	1,759,417	1,492,146
Other income (losses) , net:
Gain (loss) on divestiture and sale of investments				557
Gains (losses) on equity method investments	2,854	1,602	8,655	1,839
Other income (loss)	(810)	4,713	33,132	9,733
Total other income (losses), net	2,044	6,315	41,787	12,129
Income (loss) from operations before income taxes	65,898	94,283	199,092	152,077
Provision (benefit) for income taxes	15,908	16,552	51,671	23,230
Consolidated net income (loss)	49,990	77,731	147,421	128,847
Less: Net income (loss) attributable to noncontrolling interest in subsidiaries	14,787	24,811	53,444	39,102
Net income (loss) available to common stockholders	35,203	52,920	93,977	89,745
Basic earnings (loss) per share
Net income (loss) available to common stockholders	$ 35,039	$ 52,920	$ 93,813	$ 89,745
Basic earnings (loss) per share	$ 0.11	$ 0.18	$ 0.30	$ 0.31
Basic weighted-average shares of common stock outstanding	321,199	286,840	314,501	285,129
Fully diluted earnings (loss) per share
Net income (loss) for fully diluted shares	$ 50,445	$ 81,872	$ 139,202	$ 138,506
Fully diluted earnings (loss) per share	$ 0.10	$ 0.18	$ 0.29	$ 0.31
Fully diluted weighted-average shares of common stock outstanding	481,461	451,857	480,193	448,347
Dividends declared per share of common stock	$ 0.18	$ 0.18	$ 0.36	$ 0.34
Dividends declared and paid per share of common stock	$ 0.18	$ 0.18	$ 0.36	$ 0.34