Stock-based Compensation Plans - Additional Information 4 (Detail) - USD ($) $ in Thousands, shares in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Maximum percentage of employees contribution									75.00%
Maximum percentage of employers contribution in cash									6.00%
Employer contribution									$ 5,800	$ 5,100	$ 4,700
Deferred compensation plan vesting period									3 years
Deferred compensation plan	$ 18,072	$ (223)	$ (6,615)	$ 7,397	$ 14,077	$ 9,203	$ 14,466	$ 13,169	$ 18,631	$ 50,915	$ (19,153)
Shares held in rabbi trust total	2.6				2.9				2.6	2.9
Vested shares held in rabbi trust	2.4				2.8				2.4	2.8