Employee Benefits - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation And Retirement Disclosure [Abstract]
Maximum percentage of a participant's eligible compensation that a participating may elect to contribute, on a tax-deferred annually to the plan (as a percent) 50.00%	80.00%
Percentage of matching contribution made by company, of first 6.0% of participating employees contributions (as a percent)	50.00%
Percentage of participating employees contribution, matched 100% (as a percent)	6.00%
Employer contribution	$ 9,600	$ 9,000	$ 8,500
Non-qualified deferred gains or (losses) of investment	5,300	(700)	$ 3,700
Non-qualified deferred compensation plan assets	69,912	64,245
Non-qualified deferred compensation plan liabilities	$ 69,912	$ 64,245