Pension and Employee Benefit Plans - Components of Pension and Employee Benefit Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 101	$ 112	$ 214	$ 223
Interest cost	329	356	657	713
Expected return on plan assets	(431)	(457)	(861)	(914)
Amortization of net actuarial loss	57	53	113	106
Net periodic benefit cost	56	64	123	128
Health Care Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	2	2
Amortization of loss	2	3	4	5
Net periodic benefit cost	$ 3	$ 4	$ 6	$ 7