Employee Benefit Plans (Detail) - Net Periodic Benefit Cost (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Post Retirement Health Care and Life Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 32	$ 48	$ 96	$ 159
Interest cost	41	52	123	169
Amortization of prior service cost	(162)	(57)	(485)	(65)
Amortization of net actuarial loss	7	(79)	21	(79)
Total post-retirement benefit cost / (income)	(82)	(36)	(245)	184
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	21	51	62	153
Expected return on plan assets	(29)	(57)	(86)	(171)
Amortization of net actuarial loss	17	28	50	84
Total post-retirement benefit cost / (income)	$ 9	$ 22	$ 26	$ 66