Debt (Narrative) (Details)				3 Months Ended		9 Months Ended		12 Months Ended	86 Months Ended
	Jul. 01, 2015 USD ($)	Sep. 28, 2012 USD ($)	Sep. 27, 2012 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2016 USD ($)	Jul. 01, 2017	Jun. 15, 2013 USD ($)	Nov. 23, 2012 USD ($)	Feb. 06, 2009 USD ($)	Jan. 11, 2008 USD ($)
Debt [Line Items]
Incremental credit facility additional extension period				365 days
Percentage of principal amount of debt as component of premium price			1.00%
Senior Notes 2022
Debt [Line Items]
Debt instrument maturity date						Oct. 01, 2022
Net Proceeds From the Issuance of Long Term Debt		$ 300,000,000
Debt instrument stated interest percentage			5.25%
Long-term debt, fair value				$ 298,500,000		$ 298,500,000			$ 298,500,000
Aggregate principal value of debt			$ 300,000,000	300,000,000		300,000,000			300,000,000
Percentage of senior notes principal as part of redemption price			100.00%
York Property Mortgage Member
Debt [Line Items]
Long-term Debt and Capital Lease Obligations, Maturities, Repayments of Principal after Year Five				268,200,000		268,200,000			268,200,000
Purchase Consummated On February 6, 2009
Debt [Line Items]
Property acquisition price													$ 370,000,000
Components of purchase price of land and buildings													85,000,000
Signing Of Related Purchase And Sale Agreement On January 11, 2008
Debt [Line Items]
Components of purchase price of land and buildings														$ 50,000,000
Assumption Of Existing Mortgage
Debt [Line Items]
Components of purchase price of land and buildings													$ 235,000,000
Convertible Notes
Debt [Line Items]
Long-term Debt, Gross											$ 182,000,000
York Property Mortgage
Debt [Line Items]
Short-term debt before reclassification				310,834,000	$ 317,047,000	310,834,000	$ 317,047,000	$ 315,504,000	310,834,000
Mortgages | New Mortgage Loan
Debt [Line Items]
Debt instrument term	7 years
Aggregate principal value of debt	$ 325,000,000
Proceeds from issuance of debt	$ 98,000,000
Amortization period	25 years
Derivative contract term	7 years
Maximum LTV ratio under agreement	0.65
Escrow Deposit				6,000,000		6,000,000			6,000,000
Restricted Cash and Cash Equivalents				$ 3,600,000		$ 3,600,000			$ 3,600,000
Minimum debt yield under agreement	8.50%
Minimum net worth under agreement	$ 425,000,000
Mortgages | New Mortgage Loan | Swap
Debt [Line Items]
Derivative contract term	2 years
Fixed interest rate on hedge	0.877%
Effective interest rate	3.127%
Mortgages | New Mortgage Loan | Collar
Debt [Line Items]
Derivative contract term	5 years
Mortgages | New Mortgage Loan | One-Month LIBOR
Debt [Line Items]
Spread on variable rate	2.25%
Senior Notes
Debt [Line Items]
Long-term Debt, Gross												$ 80,000,000
Minimum | York Property Mortgage Member
Debt [Line Items]
Debt instrument stated interest percentage				5.60%		5.60%			5.60%
Minimum | Mortgages | New Mortgage Loan | Collar | Forecast
Debt [Line Items]
Fixed interest rate on hedge										1.917%
Effective interest rate										4.167%
Maximum | York Property Mortgage Member
Debt [Line Items]
Debt instrument stated interest percentage				10.60%		10.60%			10.60%
Maximum | Mortgages | New Mortgage Loan | Collar | Forecast
Debt [Line Items]
Fixed interest rate on hedge										3.75%
Effective interest rate										6.00%
New Credit Agreement
Debt [Line Items]
Line of credit facility, maximum borrowing capacity				$ 1,335,000,000	1,335,000,000	$ 1,335,000,000	1,335,000,000		$ 1,335,000,000
Increase in borrowing capacity, credit facility				485,000,000
Incremental revolving credit facility				729,517,000	860,400,000	729,517,000	860,400,000	773,228,000	729,517,000
Line of credit facility, sub-limit				400,000,000		400,000,000			400,000,000
Maximum available increase in borrowing capacity				150,000,000		150,000,000			150,000,000
Maximum amount of net auction guarantees permissible				600,000,000		600,000,000			600,000,000
Covenant, aggregate borrowing availability				100,000,000		100,000,000			100,000,000
Covenant, total liquidity amount				200,000,000		$ 200,000,000			200,000,000
Total life-to-date credit facility fees paid									21,700,000
Debt instrument maturity date						Aug. 22, 2020
Agency Credit Facility
Debt [Line Items]
Line of credit facility, maximum borrowing capacity				300,000,000	300,000,000	$ 300,000,000	300,000,000	300,000,000	300,000,000
Incremental revolving credit facility				174,548,000	$ 246,448,000	174,548,000	$ 246,448,000	$ 225,642,000	174,548,000
Line of credit facility, sub-limit				50,000,000		50,000,000			50,000,000
Incremental Credit Facility
Debt [Line Items]
Incremental revolving credit facility				$ 50,000,000		$ 50,000,000			50,000,000
SFS Credit Facility
Debt [Line Items]
Weighted-average cost of borrowing (as a percent)				3.40%	2.90%	3.30%	2.90%	2.90%
Line of credit facility, maximum borrowing capacity				$ 1,035,000,000	$ 1,035,000,000	$ 1,035,000,000	$ 1,035,000,000	$ 1,035,000,000	1,035,000,000
Incremental revolving credit facility				554,969,000	$ 613,952,000	554,969,000	$ 613,952,000	$ 547,586,000	554,969,000
Line of credit facility, sub-limit				$ 350,000,000		$ 350,000,000			$ 350,000,000
Standard & Poor's, B Rating [Member] | Mortgages | New Mortgage Loan
Debt [Line Items]
Debt Instrument, Covenant, Required Debt Service, 6 Months						12 months
Standard & Poor's, B+ Rating [Member] | Mortgages | New Mortgage Loan
Debt [Line Items]
Debt Instrument, Covenant, Required Debt Service, 6 Months						6 months