Pension and Employee Benefit Plans - Components of Pension and Employee Benefit Expenses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	$ 17	$ 15	$ 34	$ 30
Interest cost	78	82	156	164
Expected return on plan assets	(102)	(94)	(204)	(188)
Amortization of net actuarial loss	92	83	184	166
Net periodic benefit cost	85	86	170	172
Health care plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Interest cost	1	1	2	2
Amortization of gain	(4)	(2)	(8)	(4)
Net periodic benefit cost	$ (3)	$ (1)	$ (6)	$ (2)