Financing Activity (Narrative) (Detail) (USD $)	1 Months Ended	12 Months Ended			0 Months Ended	1 Months Ended						9 Months Ended	0 Months Ended
	Oct. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 28, 2014	Apr. 30, 2013	Feb. 28, 2013	May 31, 2013	Sep. 30, 2013	Oct. 31, 2013	Dec. 31, 2013	Sep. 30, 2014	Jan. 08, 2014 loan	Jan. 31, 2015	Feb. 20, 2015	Apr. 16, 2013
Debt Instrument [Line Items]
Revolving Facility		$ 0	$ 130,000,000					$ 192,500,000			$ 130,000,000
Letters of Credit Outstanding, Amount		7,100,000
Repayments of lines of credit	15,000,000
Repayment of 2010 Term Loan		130,000,000	182,000,000	58,000,000
Maximum Unsecured Borrowing Amount Under Unencumbered Debt Yield Covenant		561,100,000
Loss recognized in income on derivatives (ineffective portion and amount excluded from effectiveness testing)		(1,800,000)	3,400,000	1,200,000
The Gallery at Market East [Member]
Debt Instrument [Line Items]
Capitalization rate used to calculate Gross Asset Value						5.70%
Repayment Of mortgage secured loan					25,800,000
Moorestown Mall [Member]
Debt Instrument [Line Items]
Repayment Of mortgage secured loan							53,200,000
Available cash from working capital used to repay mortgage debt							3,200,000
Jacksonville Mall [Member]
Debt Instrument [Line Items]
Repayment Of mortgage secured loan								56,300,000
Available cash from working capital used to repay mortgage debt								21,300,000
Loss recognized in income on derivatives (ineffective portion and amount excluded from effectiveness testing)								2,900,000
Wyoming Valley Mall [Member]
Debt Instrument [Line Items]
Repayment Of mortgage secured loan									65,000,000
Exton Square Mall [Member]
Debt Instrument [Line Items]
Repayment Of mortgage secured loan										66,900,000
Revolving facility debt used to repay mortgage debt										60,000,000
Beaver Valley Mall [Member]
Debt Instrument [Line Items]
Repayment Of mortgage secured loan											42,200,000
Mortgages [Member]
Debt Instrument [Line Items]
Weighted average interest rate		4.78%
Number of real estate properties used as collateral		16
Number of loans with fixed interest rates		12
Interest rate, minimum		3.90%
Interest rate, maximum		6.34%
Mortgages [Member] | Wyoming Valley Mall [Member]
Debt Instrument [Line Items]
Face amount		78,000,000
Initial interest rate		5.17%
Mortgages [Member] | Fixed Rate Mortgages [Member]
Debt Instrument [Line Items]
Weighted average interest rate		5.05%
Mortgages [Member] | Variable Rate Mortgages [Member]
Debt Instrument [Line Items]
Weighted average interest rate		2.86%
Number of real estate properties used as collateral		4
Subsequent Event [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount														7,900,000
2013 Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Revolving Facility		0
Cost per square foot of property developed												500
2013 Revolving Facility [Member] | Jacksonville Mall [Member]
Debt Instrument [Line Items]
Revolving facility debt used to repay mortgage debt								35,000,000
2013 Revolving Facility [Member] | Wyoming Valley Mall [Member]
Debt Instrument [Line Items]
Revolving facility debt used to repay mortgage debt									65,000,000
2013 Revolving Facility [Member] | Exton Square Mall [Member]
Debt Instrument [Line Items]
Available cash from working capital used to repay mortgage debt										6,900,000
2013 Revolving Facility [Member] | Wells Fargo Bank, NA [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		400,000,000.0				400,000,000.0
Interest expense		1,500,000	2,500,000
Amortization of financing costs		1,400,000	1,100,000
Number of one year extensions		2
Accordion option, potential maximum borrowing capacity		600,000,000.0
Accordion option, minimum incremental increase		5,000,000.0
Accordion option, minimum increase		25,000,000.0
Unused capacity fee		0.30%
Percentage of gross asset value		2.50%
2013 Revolving Facility [Member] | Wells Fargo Bank, NA [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		1.70%
2013 Revolving Facility [Member] | Wells Fargo Bank, NA [Member] | LIBOR [Member] | Less than 0.450 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		1.50%
2013 Revolving Facility [Member] | Wells Fargo Bank, NA [Member] | LIBOR [Member] | Equal to or greater than 0.450 to 1.00 but less than 0.500 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		1.70%
2013 Revolving Facility [Member] | Wells Fargo Bank, NA [Member] | LIBOR [Member] | Equal to or greater than 0.500 to 1.00 but less than 0.550 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		1.85%
2013 Revolving Facility [Member] | Wells Fargo Bank, NA [Member] | LIBOR [Member] | Equal to or greater than 0.550 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		2.05%
2013 Revolving Facility [Member] | Wells Fargo Bank, NA [Member] | Minimum [Member]
Debt Instrument [Line Items]
Term extension fee		0.15%
Capitalization rate used to calculate Gross Asset Value		6.50%
2013 Revolving Facility [Member] | Wells Fargo Bank, NA [Member] | Minimum [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		1.50%
2013 Revolving Facility [Member] | Wells Fargo Bank, NA [Member] | Maximum [Member]
Debt Instrument [Line Items]
Term extension fee		0.20%
Capitalization rate used to calculate Gross Asset Value		7.50%
2013 Revolving Facility [Member] | Wells Fargo Bank, NA [Member] | Maximum [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		2.05%
2013 Revolving Facility [Member] | Wells Fargo Bank, NA [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Remaining borrowing capacity															0
2010 Revolving Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity																250,000,000.0
Repayments of lines of credit		95,000,000
Interest expense			400,000	2,600,000
2010 Revolving Facility [Member] | Moorestown Mall [Member]
Debt Instrument [Line Items]
Revolving facility debt used to repay mortgage debt							50,000,000
2010 Term Loan [Member]
Debt Instrument [Line Items]
Revolving Facility																97,500,000
Weighted average interest rate		3.95%	4.82%								4.82%
Repayment of 2010 Term Loan			182,000,000	58,000,000
Interest expense			2,400,000	14,400,000
2010 Term Loan [Member] | 2013 Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Repayment of 2010 Term Loan		97,500,000
2014 Term Loans [Member]
Debt Instrument [Line Items]
Amortization of financing costs		300,000
Cost per square foot of property developed													500
Percentage of gross asset value													2.50%
Number of loan entered during period													2
Face amount													250,000,000.0
Interest expense		4,700,000
2014 Term Loans [Member] | Minimum [Member]
Debt Instrument [Line Items]
Capitalization rate used to calculate Gross Asset Value													6.50%
2014 Term Loans [Member] | Maximum [Member]
Debt Instrument [Line Items]
Capitalization rate used to calculate Gross Asset Value													7.50%
5 Year Term Loan [Member]
Debt Instrument [Line Items]
Revolving Facility		100,000,000
Debt Instrument, Interest Rate, Effective Percentage		1.61%
5 Year Term Loan [Member] | Wells Fargo Bank, NA and US Bank N [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity													150,000,000.0
Accordion option, potential maximum borrowing capacity													300,000,000.0
Accordion option, minimum incremental increase													5,000,000.0
Accordion option, minimum increase													25,000,000.0
Unused capacity fee													0.20%
Face amount													150,000,000.0
Term													5 years
5 Year Term Loan [Member] | Wells Fargo Bank, NA and US Bank N [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate													1.45%
5 Year Term Loan [Member] | Wells Fargo Bank, NA and US Bank N [Member] | LIBOR [Member] | Less than 0.450 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate													1.35%
5 Year Term Loan [Member] | Wells Fargo Bank, NA and US Bank N [Member] | LIBOR [Member] | Equal to or greater than 0.450 to 1.00 but less than 0.500 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate													1.45%
5 Year Term Loan [Member] | Wells Fargo Bank, NA and US Bank N [Member] | LIBOR [Member] | Equal to or greater than 0.500 to 1.00 but less than 0.550 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate													1.60%
5 Year Term Loan [Member] | Wells Fargo Bank, NA and US Bank N [Member] | LIBOR [Member] | Equal to or greater than 0.550 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate													1.90%
7 Year Term Loan [Member]
Debt Instrument [Line Items]
Revolving Facility		30,000,000
Debt Instrument, Interest Rate, Effective Percentage		2.11%
7 Year Term Loan [Member] | Wells Fargo Bank, NA and Capital One, NA [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity													100,000,000.0
Accordion option, potential maximum borrowing capacity													200,000,000.0
Accordion option, minimum incremental increase													5,000,000.0
Accordion option, minimum increase													25,000,000.0
Unused capacity fee													0.35%
Face amount													100,000,000.0
Term													7 years
Prepayment penalty year one													3.00%
Prepayment penalty year two													2.00%
Prepayment penalty year three													1.00%
7 Year Term Loan [Member] | Wells Fargo Bank, NA and Capital One, NA [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate													1.95%
7 Year Term Loan [Member] | Wells Fargo Bank, NA and Capital One, NA [Member] | LIBOR [Member] | Less than 0.450 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate													1.80%
7 Year Term Loan [Member] | Wells Fargo Bank, NA and Capital One, NA [Member] | LIBOR [Member] | Equal to or greater than 0.450 to 1.00 but less than 0.500 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate													1.95%
7 Year Term Loan [Member] | Wells Fargo Bank, NA and Capital One, NA [Member] | LIBOR [Member] | Equal to or greater than 0.500 to 1.00 but less than 0.550 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate													2.15%
7 Year Term Loan [Member] | Wells Fargo Bank, NA and Capital One, NA [Member] | LIBOR [Member] | Equal to or greater than 0.550 to 1.00 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate													2.35%
2014 Term Loans and 2013 Revolving Facility [Member]
Debt Instrument [Line Items]
Percentage of distribution related to FFO		95.00%
Minimum tangible net worth		75.00%
Net proceeds of equity issuance		75.00%
Maximum secured indebtedness		0.60
Unencumbered debt yield		12.00%
Investment value of gross asset value		1.75
Maximum ratio of secured indebtedness to gross asset value		0.60
Maximum investments in unimproved real estate and predevelopments costs		5.00%
Maximum investments in persons other than subsidiaries, consolidated affiliates and unconsolidated affiliates		5.00%
Maximum mortgages in favor of the borrower or any other subsidiary		5.00%
Maximum aggregate value of investments to gross asset value		10.00%
Maximum investments in consolidation exempt entities to gross asset value		25.00%
Maximum projects under development to gross asset value		15.00%
Percentage of distribution related to FFO		35.00%
REIT taxable income distributions		110.00%
2014 Term Loans and 2013 Revolving Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Maximum secured indebtedness		0.60
2014 Term Loans and 2013 Revolving Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Maximum secured indebtedness		0.625
Minimum ratio of adjusted EBITDA to fixed charges		1.50
2010 Credit Facility [Member]
Debt Instrument [Line Items]
Amortization of financing costs			800,000	3,500,000
Accelerated deferred financing fees			$ 900,000	$ 700,000