Employee Benefit Plans (Detail) - Net Periodic Benefit Cost (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Post Retirement Health Care and Life Benefits [Member]
Service cost	$ 31	$ 56	$ 64	$ 112
Interest cost	39	59	82	118
Amortization of prior service cost	(156)	(4)	(323)	(8)
Amortization of net actuarial loss	6	0	14	0
Total post-retirement benefit cost / (income)	(80)	111	(163)	222
Pension Benefits [Member]
Interest cost	21	51	42	102
Expected return on plan assets	(28)	(57)	(57)	(114)
Amortization of net actuarial loss	16	28	33	56
Total post-retirement benefit cost / (income)	$ 9	$ 22	$ 18	$ 44