Employee Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Executive Retirement Health Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		$ 174	$ 649
Interest cost		78	134
Amortization of actuarial loss		0	86
Settlement/curtailment loss/(gain)		725	(359)
Net periodic benefit (gain) cost		977	510
Supplemental Executive Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1,323	1,164	2,018
Interest cost	383	294	471
Amortization of actuarial loss	0	0	97
Settlement loss	0	0	24
Net periodic benefit (gain) cost	$ 1,706	$ 1,458	$ 2,610