Notes Receivable from Employees - Additional information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) note	Dec. 31, 2017 USD ($) note	Dec. 31, 2016 USD ($)
Receivables [Abstract]
Notes outstanding (in notes) | note	294	270
Amortization of forgivable loan expense | $	$ 36.4	$ 26.8	$ 25.6