Retirement and Deferred Compensation Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Contribution to defined plans	$ 2.6	$ 1.8	$ 1.9
Non-qualified deferred cash incentive plan maximum eligibility percentage of employees	100.00%
Mutual fund investments and deferred compensation obligation, at fair value	$ 4.1	3.2
Trading (losses) gains and changes in deferred compensation liability and expense	$ (0.2)	$ 0.4	$ 0.2