Subsequent Events (Details) (Subsequent Event [Member], USD $) In Millions, unless otherwise specified	1 Months Ended
	Jan. 31, 2013 Common Stock [Member]	Jan. 31, 2013 Land [Member]	Jan. 31, 2013 Acquisition I [Member]	Feb. 28, 2013 Acquisition II [Member] sqft
Subsequent Event [Line Items]
Number of units			56	444
Subsequent event, amount	$ 20.3	$ 9.1	$ 19.0	$ 135.0
Gain on sale of land parcel held for future development		1.5
Gain on sale of common stock investment	$ 1.8
Number of floors of acquired property				29
Number of floors of commercial office excluded from acquired property				12
Number of floors of underground parking garage included from acquired property				2
Number of stalls in underground parking included in acquired property included from acquired property				405
Subsequent Events Area Acquired				37,800