Employee Benefit Plans - Components of Net Periodic Benefit Cost (Gain) (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Pension Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost	$ 62	$ 69
Expected return on plan assets	(90)	(96)
Settlement loss	26
Recognized net actuarial loss	38	39
Net periodic cost	36	12
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	10	11
Interest cost	10	14
Amortization of net gain	(4)
Net periodic cost	$ 16	$ 25