Retirement and Postretirement Benefits Other than Pension Plans - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	May 31, 2013	Dec. 31, 2012
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net settlement loss	$ (200,000)	$ (1,500,000)
Changed in assumed discount rate			4.00%	3.60%
Reduction in plan liability		9,500,000
REIT Conversion [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net settlement loss		(700,000)
Corporate Operating Expenses [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net settlement loss	$ (200,000)	$ (800,000)