Investments in Joint Ventures (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2010 Sherman [Member]	Dec. 31, 2008 Sherman [Member]	Aug. 31, 2008 Sherman [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage (in hundredths)						24.25%
Cash proceeds from sale of investment in joint venture					$ 124,500,000
Unsecured promissory note received as consideration in sale of investment in joint venture					85,000,000
Scheduled maturity of unsecured promissory note					Feb. 13, 2011
Variable rate basis of unsecured promissory note					three-month LIBOR
Basis spread on variable rate of unsecured promissory note (in basis points)					500
Proceeds from unsecured promissory note	0	0	83,500,000	83,500,000
Carrying value of unsecured promissory note				84,000,000
Loss recognized on unsecured promissory note	$ 0	$ 0	$ (466,000)	$ 500,000