Investment in Unconsolidated Joint Ventures (Palisades West LLC) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Equity Method Investments [Line Items]
Gain on sale of investment properties	$ 15,001	$ 12,013	$ 9,164
Palisades West LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage equity method investment (percent)	50.00%
Ownership percentage by noncontrolling owners (percent)	50.00%
Gain on sale of investment properties	$ 23,300
Building [Member] | Palisades West LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of real estate properties owned by venture (properties)	2
TEXAS
Schedule of Equity Method Investments [Line Items]
Number of real estate properties owned by venture (properties)	1
TEXAS | Palisades West LLC [Member]
Schedule of Equity Method Investments [Line Items]
Square footage of real estate property (square feet)	373,000