Retirement and Postretirement Benefits Other than Pension Plans - Net Periodic Pension and Postretirement Benefit Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 993	$ 1,087
Expected return on plan assets	(1,291)	(1,173)
Amortization of net actuarial loss	318	1,170
Total net periodic pension expense	20	1,084
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		14
Interest cost	64	254
Amortization of net actuarial loss	96	176
Amortization of prior service credit	(285)	(130)
Total net postretirement benefit expense	$ (125)	$ 314