Condensed Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Accounts receivable, allowances	$ 1,212	$ 1,117
Property, equipment and leasehold improvements, accumulated depreciation and amortization	133,237	114,680
Intangible assets, accumulated amortization	$ 451,990	$ 418,512
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	750,000,000	750,000,000
Common stock, shares issued	128,955,118	128,200,189
Common stock, shares outstanding	94,672,958	101,013,148
Treasury shares	34,282,160	27,187,041