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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Other Postretirement Benefit Plans, Defined Benefit [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Interest cost	$ 54	$ 33	$ 109	$ 97
Amortization of net actuarial loss	104	142	209	238
Amortization of prior service credit	(328)	(380)	(657)	(665)
Total net postretirement benefit income	(170)	(205)	(339)	(330)
Pension Plans, Defined Benefit [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Interest cost	1,045	947	2,089	1,940
Expected return on plan assets	(1,410)	(1,283)	(2,819)	(2,574)
Recognized net actuarial loss	147	262	295	580
Net settlement loss		1,290		1,290
Total net periodic pension (income) expense	$ (218)	$ 1,216	$ (435)	$ 1,236