Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Tax Examination [Line Items]
Provision for income taxes	$ 28,674	$ 30,410
Effective tax rate	28.20%	33.50%
Amounts effect on effective tax rate	$ 3,500
Decrease in effective tax rate	3.50%
Significant change in unrecognized tax benefits, reasonably possible	It is reasonably possible that significant changes in the balance of unrecognized tax benefits may occur within the next 12 months.
Significant change in unrecognized tax benefits, not possible	At this time, however, it is not possible to reasonably estimate the expected change to the total amount of unrecognized tax benefits and the impact on the effective tax rate over the next 12 months.
Minimum [Member]
Income Tax Examination [Line Items]
Tax years under examination	2005
Maximum [Member]
Income Tax Examination [Line Items]
Tax years under examination	2016
State and Local Jurisdiction [Member] | New York State Division of Taxation and Finance [Member] | Minimum [Member] | Morgan Stanley [Member]
Income Tax Examination [Line Items]
Tax years under examination	2007
State and Local Jurisdiction [Member] | New York State Division of Taxation and Finance [Member] | Maximum [Member] | Morgan Stanley [Member]
Income Tax Examination [Line Items]
Tax years under examination	2008
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | Minimum [Member] | Morgan Stanley [Member]
Income Tax Examination [Line Items]
Tax years under examination	2006
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | Maximum [Member] | Morgan Stanley [Member]
Income Tax Examination [Line Items]
Tax years under examination	2008