Pension and Employee Benefit Plans - Components of Pension and Employee Benefit Expenses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 58	$ 50
Interest cost	354	357
Expected return on plan assets	(502)	(488)
Amortization of net actuarial loss	65	44
Net periodic benefit cost (gain)	(25)	(37)
Health Care Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1
Amortization of loss (gain)	2	(1)
Net periodic benefit cost (gain)	$ 3