Condensed Consolidated Statements of Financial Condition (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Class A Common Stock [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	750,000,000	750,000,000
Common stock, shares issued	341,030,000	306,218,000
Common stock, shares outstanding	290,910,000	256,968,000
Treasury stock, at cost	50,120,000	49,250,000
Class B Common Stock [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	34,848,000	34,848,000
Common stock, shares outstanding	34,848,107	34,848,000