Capital and Financing Transactions Notes Payable (Details) (USD $)				6 Months Ended						0 Months Ended	6 Months Ended		0 Months Ended	6 Months Ended				6 Months Ended				6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013 Term Loan [Member]	Jun. 30, 2013 Working Capital Revolving Credit Facility [Member]	Jun. 30, 2013 Working Capital Revolving Credit Facility [Member] PNC Bank [Member]		Jun. 30, 2013 Unsecured Revolving Credit Facility [Member] Wells Fargo Bank [Member]		Jun. 30, 2013 Unsecured Term Loan $125 million [Member] Key Bank [Member]		Jun. 12, 2013 Unsecured Term Loan $120 million [Member] Wells Fargo Bank [Member]	Jun. 30, 2013 Unsecured Term Loan $120 million [Member] Wells Fargo Bank [Member]		Sep. 28, 2012 Term Loan Swap [Member] Swap	Jun. 30, 2013 London Interbank Offered Rate (LIBOR) [Member] Working Capital Revolving Credit Facility [Member]	Jun. 12, 2013 London Interbank Offered Rate (LIBOR) [Member] Working Capital Revolving Credit Facility [Member]	Jun. 30, 2013 London Interbank Offered Rate (LIBOR) [Member] Unsecured Term Loan $125 million [Member]	Sep. 28, 2012 London Interbank Offered Rate (LIBOR) [Member] Term Loan Swap [Member]	Jun. 30, 2013 Minimum [Member] Working Capital Revolving Credit Facility [Member]	Jun. 30, 2013 Minimum [Member] London Interbank Offered Rate (LIBOR) [Member] Working Capital Revolving Credit Facility [Member]	Jun. 30, 2013 Minimum [Member] London Interbank Offered Rate (LIBOR) [Member] Unsecured Term Loan $125 million [Member]	Jun. 30, 2013 Minimum [Member] London Interbank Offered Rate (LIBOR) [Member] Unsecured Term Loan $120 million [Member]	Jun. 30, 2013 Maximum [Member] Working Capital Revolving Credit Facility [Member]	Jun. 30, 2013 Maximum [Member] London Interbank Offered Rate (LIBOR) [Member] Working Capital Revolving Credit Facility [Member]	Jun. 30, 2013 Maximum [Member] London Interbank Offered Rate (LIBOR) [Member] Unsecured Term Loan $125 million [Member]	Jun. 30, 2013 Maximum [Member] London Interbank Offered Rate (LIBOR) [Member] Unsecured Term Loan $120 million [Member]	Jun. 30, 2013 Mortgages [Member]
Debt Instrument [Line Items]
Modified mortgage loan																										$ 724,100,000
Interest Rate	2.40%			0.00%	[1]	1.80%	[1]	2.20%	[2]	3.10%	3.10%	[3]					0.70%
Maturity				Mar. 29, 2016		Mar. 29, 2016		Sep. 27, 2017		Jun. 11, 2018	Jun. 11, 2018
Outstanding Balance	313,000,000	245,000,000		0		68,000,000		125,000,000		120,000,000	120,000,000
LIBOR														LIBOR
Basis spread on variable rate (in percent)																			1.60%	1.50%	1.45%		2.35%	2.30%	2.00%
LIBOR rate period fixed (in percent)														1.60%	1.60%	1.50%					1.45%
Number of interest rate swaps													2
Commitment fee percentage (in percent)																		0.25%				0.35%
Commitment fee percentage for the current period (in percent)			0.35%
Notional amount								125,000,000.0			120,000,000		125,000,000
Term loan swap term (in years)										5 years			5 years
Maximum borrowing capacity										$ 250,000,000

[1] The interest rate on the credit facilities is based on LIBOR plus an applicable margin of 160 basis point to 235 basis points, depending upon overall Company leverage as defined in the loan agreements for the Company's credit facilities, with the current rate set at 160 basis points. Additionally, the Company pays fees on the unused portion of the credit facilities ranging between 25 and 35 basis points based upon usage of the aggregate commitment, with the current rate set at 35 basis points.

[2] The interest rate on the term loan is based on LIBOR plus an applicable margin of 150 to 230 basis points depending on overall Company leverage (with the current rate set at 150 basis points). On September 28, 2012, the Company executed two floating-to-fixed interest rate swaps totaling $125 million, locking LIBOR at 0.7% for five years which was effective October 1, 2012.

[3] The interest rate on the term loan is based on LIBOR plus an applicable margin of 145 to 200 basis points depending on overall Company leverage (with the current rate set at 145 basis points). On June 12, 2013, the Company executed a floating-to-fixed interest rate swap totaling $120 million, locking LIBOR at 1.6% for five years.