Employee Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Executive Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1,310	$ 1,323	$ 1,164
Interest cost	453	383	294
Net periodic benefit (gain) cost	$ 1,763	$ 1,706	1,458
Supplemental Executive Retirement Health Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost			174
Interest cost			78
Settlement/curtailment loss			725
Net periodic benefit (gain) cost			$ 977