Retirement and Deferred Compensation Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation And Retirement Disclosure [Abstract]
Contribution to defined plans	$ 1.9	$ 1.9	$ 1.8
Non-qualified deferred cash incentive plan maximum eligibility percentage of employees		100.00%
Mutual fund investments and deferred compensation obligation, at fair value	1.3
Trading gain and compensation expense	$ 0.2