Stock-based Compensation Plans - Additional Information 4 (Detail) - USD ($) shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation plan vesting period			3 years
Deferred compensation plan	$ (6,615,000)	$ 14,466,000	$ 782,000	$ 27,635,000
Shares held in rabbi trust total	3.1		3.1		2.9
Vested shares held in rabbi trust	2.9		2.9		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			$ 185,000