Retirement and Postretirement Benefits Other Than Pension Plans - Net Periodic Pension and Postretirement Benefit (Income) Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Other Postretirement Benefit Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Interest cost	$ 56	$ 49	$ 165	$ 146
Amortization of net actuarial loss	125	120	334	358
Amortization of prior service credit	(328)	(333)	(985)	(998)
Total net postretirement benefit income	(147)	(164)	(486)	(494)
Pension Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Interest cost	1,053	999	3,142	2,939
Expected return on plan assets	(1,379)	(1,312)	(4,198)	(3,886)
Recognized net actuarial loss	180	242	475	822
Net settlement loss		188		1,478
Total net periodic pension (income) expense	$ (146)	$ 117	$ (581)	$ 1,353