Secured and unsecured senior debt (Details 2) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Secured construction loan
Total consolidated debt	2,998,760
259 East Grand Avenue
Secured construction loan
Percentage of project pre-leased	100.00%
Rentable square feet, development properties (in square feet)	170,618
Secured construction loan due in June 2017 | LIBOR
Secured construction loan
Base rate	LIBOR
Applicable margin (as a percent)	1.50%
Secured construction loan due in June 2017 | Base Rate
Secured construction loan
Base rate	Base Rate
Applicable margin (as a percent)	0.25%
Secured construction loan due in June 2017 | 259 East Grand Avenue
Secured construction loan
Total consolidated debt	55,000