Derivatives (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended			1 Months Ended	12 Months Ended				12 Months Ended			1 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Logan Valley Mall [Member]	May 31, 2013 Interest Expense [Member]	Dec. 31, 2013 Interest Expense [Member]	Dec. 31, 2012 Interest Expense [Member]	Dec. 31, 2011 Interest Expense [Member]	Jan. 31, 2014 Subsequent Event [Member] Agreement	Dec. 31, 2013 Interest rate swap [Member] Agreement	Dec. 31, 2013 Interest rate swap [Member] 2010 Credit Facility [Member] Agreement	Jan. 31, 2014 Interest rate swap [Member] Subsequent Event [Member]	May 31, 2013 Forward Starting Swap [Member]	Dec. 31, 2013 Interest Rate Swap Twelve [Member]
Derivative Instruments [Line Items]
Estimate increase to interest expense	$ 2.5
Number of derivative, interest rate swap agreement								6	6	3
Derivative, Weighted average interest rate									1.61%		1.78%
Derivative, notional amount									198.6	40.0	130.0
Loss recognized in income on derivatives (ineffective portion and amount excluded from effectiveness testing)	3.4	1.2	0.5		3.4	1.2	0					2.9
Accelerated amortization expense			0.5
Loss reclassified from Accumulated Other Comprehensive Income (Loss) into income (effective portion)	4.4			2.9	(9.9)	(18.8)	(17.2)
Derivative, Maturity Date													Jan. 01, 2018
Deferred losses in other comprehensive income										0.6
Swap expiration date										March 2013
Derivative, interest expense	0.6
Period of amortization									10 years
Fair value of derivatives in a net liability position	(0.1)
Termination value	$ (0.2)