Stock-based Compensation Plans - Additional Information 4 (Detail) - USD ($) shares in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation plan vesting period	3 years
Deferred compensation plan	$ 7,397,000	$ 13,169,000
Shares held in rabbi trust total	3.5		2.9
Vested shares held in rabbi trust	3.3		2.8
Post-Retirement Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Estimated prior service cost amortized from accumulated other comprehensive income into general and administrative expense	$ 92,000