Capital and Financing Transactions Notes Payable (Details) (USD $)				9 Months Ended						0 Months Ended	9 Months Ended		0 Months Ended	9 Months Ended				9 Months Ended				9 Months Ended				0 Months Ended
	Sep. 30, 2013	Sep. 30, 2013 Term Loan	Sep. 30, 2013 Working Capital Revolving Credit Facility	Sep. 30, 2013 Working Capital Revolving Credit Facility PNC Bank		Sep. 30, 2013 Unsecured Revolving Credit Facility Wells Fargo Bank		Sep. 30, 2013 Unsecured Term Loan $125 million Key Bank		Jun. 12, 2013 Unsecured Term Loan $120 million Wells Fargo Bank	Sep. 30, 2013 Unsecured Term Loan $120 million Wells Fargo Bank		Sep. 28, 2012 Term Loan Swap Swap	Sep. 30, 2013 LIBOR Working Capital Revolving Credit Facility	Jun. 12, 2013 LIBOR Working Capital Revolving Credit Facility	Sep. 30, 2013 LIBOR Unsecured Term Loan $125 million	Sep. 28, 2012 LIBOR Term Loan Swap	Sep. 30, 2013 Minimum Working Capital Revolving Credit Facility	Sep. 30, 2013 Minimum LIBOR Working Capital Revolving Credit Facility	Sep. 30, 2013 Minimum LIBOR Unsecured Term Loan $125 million	Sep. 30, 2013 Minimum LIBOR Unsecured Term Loan $120 million	Sep. 30, 2013 Maximum Working Capital Revolving Credit Facility	Sep. 30, 2013 Maximum LIBOR Working Capital Revolving Credit Facility	Sep. 30, 2013 Maximum LIBOR Unsecured Term Loan $125 million	Sep. 30, 2013 Maximum LIBOR Unsecured Term Loan $120 million	Jun. 28, 2013 Hayden Ferry Lakeside II Hayden Ferry II Modified Mortgage LIBOR	Jun. 28, 2013 Hayden Ferry Lakeside II Hayden Ferry II Modified Mortgage Minimum LIBOR	Jun. 28, 2013 Hayden Ferry Lakeside II Hayden Ferry II Modified Mortgage Maximum LIBOR
Debt Instrument [Line Items]
Interest Rate	2.30%			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	$ 391,000,000	$ 245,000,000		$ 0		$ 146,000,000		$ 125,000,000		$ 120,000,000	$ 120,000,000
LIBOR														LIBOR												LIBOR
Basis spread on variable rate (in percent)																			1.60%	1.50%	1.45%		2.35%	2.30%	2.00%		2.50%	3.50%
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 25 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 which was effective June 12, 2013.