Condensed Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Accounts receivable, allowances	$ 1,108	$ 1,035
Property, equipment and leasehold improvements, accumulated depreciation and amortization	146,219	136,841
Intangible assets, accumulated amortization	$ 474,276	$ 462,860
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	129,385,707	128,996,344
Common stock, shares outstanding	90,450,616	91,279,590
Treasury shares	38,935,091	37,716,754