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Properties encumbered mortgage indebtedness carrying value, net

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Amount of noncash expense included in interest expense to issue debt and obtain financing associated with the related debt instruments. Alternate captions include noncash interest expense.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Description of debt redemption features under terms of the debt agreement.

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Face (par) amount of the original debt instrument that was repurchased.

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Average fixed interest rate related to the group of interest rate derivatives.

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The cash outflow for the extinguishment of long-term borrowing, with the highest claim on the assets of the entity in case of bankruptcy or liquidation, before its maturity.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Debt Obligations (Details Textuals) (USD $)	0 Months Ended	12 Months Ended
Debt Obligations (Details Textuals) (USD $)	Sep. 16, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt obligations (Textuals)
Early Repayment of Senior Debt		$ 383,768,000us-gaap_EarlyRepaymentOfSeniorDebt	$ 31,369,000us-gaap_EarlyRepaymentOfSeniorDebt	$ 338,097,000us-gaap_EarlyRepaymentOfSeniorDebt
Amortization of Financing Costs		5,148,000us-gaap_AmortizationOfFinancingCosts	4,676,000us-gaap_AmortizationOfFinancingCosts	6,208,000us-gaap_AmortizationOfFinancingCosts
Loss on early extinguishment of debt	(2,606,000)	(7,594,000)	(2,119,000)	(22,002,000)
Unsecured Debt [Member]
Debt obligations (Textuals)
Long-term Debt, Gross		1,803,529,000	1,929,703,000
Secured Debt [Member]
Participating Mortgage Loans [Line Items]
Properties encumbered mortgage indebtedness carrying value, net		655,900,000	669,800,000
Debt obligations (Textuals)
Long-term Debt, Gross		655,934,000	669,762,000
Letter of Credit [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.50%
Debt obligations (Textuals)
Letters of credit outstanding		4,300,000
New Revolving Credit Facility [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.50%
Debt obligations (Textuals)
Unused availability under the Credit Facility		595,700,000
Note 2023 [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.95%
Debt obligations (Textuals)
Debt instrument, face amount		250,000,000
Long-term Debt, Gross		250,000,000	250,000,000
$300.0M 5.750% Guaranteed Notes due 2012 [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		5.75%
$250.0M 5.400% Guaranteed Notes due 2014 [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Redemption, Description	$1,026.88 per $1,000
Debt Instrument, Repurchased Face Amount	143,500,000
Debt Instrument, Interest Rate, Stated Percentage		5.40%
Debt obligations (Textuals)
Debt instrument, face amount		250,000,000
Long-term Debt, Gross		0	218,549,000
$250.0M 7.500% Guaranteed Notes due 2015 [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Redemption, Description	$1,070.24 per $1,000
Debt Instrument, Repurchased Face Amount	114,900,000
Debt Instrument, Interest Rate, Stated Percentage		7.50%
Debt obligations (Textuals)
Debt instrument, face amount		250,000,000
Long-term Debt, Gross		0	157,625,000
Loss on early extinguishment of debt		(5,000,000)
$250.0M 6.000% Guaranteed Notes due 2016 [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		6.00%
Debt obligations (Textuals)
Debt instrument, face amount		250,000,000
Long-term Debt, Gross		149,919,000	149,919,000
$300.0M 5.700% Guaranteed Notes due 2017 [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		5.70%
Debt obligations (Textuals)
Debt instrument, face amount		300,000,000
Long-term Debt, Gross		300,000,000	300,000,000
$325.0M 4.950% Guaranteed Notes due 2018 [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.95%
Debt obligations (Textuals)
Debt instrument, face amount		325,000,000
Long-term Debt, Gross		325,000,000	325,000,000
Three Year Term Loan [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Repurchased Face Amount	150,000,000
Debt obligations (Textuals)
Long-term Debt, Gross		0	150,000,000
Seven Year Term Loan [Member] \| Unsecured Debt [Member]
Debt obligations (Textuals)
Debt instrument, face amount		200,000,000
Derivative, Average Fixed Interest Rate		3.623%
Long-term Debt, Gross		200,000,000	200,000,000
Note 2024 [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.10%
Debt obligations (Textuals)
Debt instrument, face amount		250,000,000
Long-term Debt, Gross		250,000,000	0
Note 2029 [Member] \| Unsecured Debt [Member]
Participating Mortgage Loans [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.55%
Debt obligations (Textuals)
Debt instrument, face amount		250,000,000
Long-term Debt, Gross		250,000,000	0
Subsidiaries [Member]
Debt obligations (Textuals)
Early Repayment of Senior Debt		383,768,000	31,369,000	338,097,000
Amortization of Financing Costs		5,148,000	4,676,000	6,208,000
Loss on early extinguishment of debt		(7,594,000)	(2,119,000)	(22,002,000)
Subsidiaries [Member] \| $300.0M 5.750% Guaranteed Notes due 2012 [Member]
Debt obligations (Textuals)
Early Repayment of Senior Debt				$ 151,200,000