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		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Net settlement loss	$ 200		$ 1,500
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		14		43
Interest cost	49	254	146	761
Amortization of net actuarial loss	120	176	358	528
Amortization of prior service credit	(333)	(130)	(998)	(391)
Total net postretirement benefit expense	(164)	314	(494)	941
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	999	1,086	2,939	3,260
Expected return on plan assets	(1,312)	(1,173)	(3,886)	(3,519)
Amortization of net actuarial loss	242	1,170	822	3,510
Net settlement loss	188		1,478
Total net periodic pension expense	$ 117	$ 1,083	$ 1,353	$ 3,251