Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule Of Pre Tax Income [Line Items]
Excess tax benefits on share based payments	$ 1.8	$ 5.8
U.S. federal tax at statutory rate	21.00%		35.00%
Provisional tax charge recorded due to enactment of Tax Act	$ 11.7
Re-measurement of U.S. deferred tax assets	6.7
Repatriation taxes on accumulated undistributed foreign earnings	$ 5.0
New York State [Member] | Earliest Tax Year [Member]
Schedule Of Pre Tax Income [Line Items]
Income tax year under examination	2010
New York State [Member] | Latest Tax Year [Member]
Schedule Of Pre Tax Income [Line Items]
Income tax year under examination	2013