Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenues:
Commissions	$ 580,033	$ 498,588	$ 1,127,159	$ 973,675
Principal transactions	80,360	86,448	166,103	178,887
Real estate management services	51,589	45,529	102,219	91,587
Fees from related parties	5,576	4,865	12,141	11,935
Data, software and post-trade	13,322	14,160	26,409	28,094
Interest income	6,001	3,778	9,304	6,162
Other revenues	876	402	1,852	4,084
Total revenues	737,757	653,770	1,445,187	1,294,424
Expenses:
Compensation and employee benefits	454,099	420,264	891,590	830,539
Allocations of net income and grant of exchangeability to limited partnership units and FPUs	50,237	40,975	113,430	73,899
Total compensation and employee benefits	504,336	461,239	1,005,020	904,438
Occupancy and equipment	49,296	50,963	99,159	102,658
Fees to related parties	5,404	3,642	11,781	9,967
Professional and consulting fees	20,736	14,336	40,316	30,054
Communications	31,915	31,281	63,609	62,579
Selling and promotion	29,389	25,546	52,774	51,204
Commissions and floor brokerage	10,203	10,097	20,373	19,140
Interest expense	16,676	14,624	31,497	28,082
Other expenses	30,759	23,713	58,747	46,554
Total expenses	698,714	635,441	1,383,276	1,254,676
Other income (losses) , net:
Gain (loss) on divestiture and sale of investments			557
Gains (losses) on equity method investments	1,602	863	1,839	1,751
Other income (loss)	4,855	10,012	9,944	7,095
Total other income (losses), net	6,457	10,875	12,340	8,846
Income (loss) from operations before income taxes	45,500	29,204	74,251	48,594
Provision (benefit) for income taxes	16,547	10,548	23,206	15,388
Consolidated net income (loss)	28,953	18,656	51,045	33,206
Less: Net income (loss) attributable to noncontrolling interest in subsidiaries	7,185	4,189	11,062	6,234
Net income (loss) available to common stockholders	21,768	14,467	39,983	26,972
Basic earnings (loss) per share
Net income (loss) available to common stockholders	$ 21,768	$ 14,467	$ 39,983	$ 26,972
Basic earnings (loss) per share	$ 0.08	$ 0.05	$ 0.14	$ 0.10
Basic weighted-average shares of common stock outstanding	286,840	275,997	285,129	274,895
Fully diluted earnings (loss) per share
Net income (loss) for fully diluted shares	$ 33,094	$ 23,452	$ 60,704	$ 43,904
Fully diluted earnings (loss) per share	$ 0.07	$ 0.05	$ 0.14	$ 0.10
Fully diluted weighted-average shares of common stock outstanding	451,857	437,257	448,347	435,963
Dividends declared per share of common stock	$ 0.18	$ 0.16	$ 0.34	$ 0.30
Dividends declared and paid per share of common stock	$ 0.18	$ 0.16	$ 0.34	$ 0.30