Employee Benefit Plans - Components of Net Periodic Benefit Cost (Gain) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost	$ 31	$ 35
Expected return on plan assets	(45)	(48)
Settlement loss	13
Recognized net actuarial loss	19	19
Net periodic cost	18	6
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	5	6
Interest cost	5	7
Amortization of net gain	(2)
Net periodic cost	$ 8	$ 13