Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 38	$ 66	$ 65
Interest cost	46	91	119
Expected return on plan assets	(11)	(10)	(17)
Amortization of prior service cost	69	65	76
Amortization of net transition obligation	22	0	(1)
Amortization of plan loss	0	0	28
Recognized actuarial net loss	0	17	14
Curtailments	0	0	160
Net periodic pension benefit cost	$ 164	$ 229	$ 444