Secured and unsecured senior debt (Details 2) (USD $) In Thousands, unless otherwise specified			9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 259 East Grand Avenue sqft	Sep. 30, 2012 Secured construction loan due in July 2015 LIBOR	Sep. 30, 2012 Secured construction loan due in July 2015 Base Rate	Sep. 30, 2012 Secured construction loan due in July 2015 259 East Grand Avenue	Jun. 30, 2012 Secured construction loan due in July 2015 259 East Grand Avenue
Secured construction loan
Total consolidated debt	$ 3,032,144				$ 53,000	$ 55,000
Percentage of project pre-leased		100.00%
Rentable square feet, development properties (in square feet)		170,618
Base rate			LIBOR	Base Rate
Applicable margin (as a percent)			1.50%	0.25%