Secured and unsecured senior debt Interest Expense (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Interest expense incurred
Gross interest	$ 32,959	$ 33,855	$ 96,668	$ 99,094
Capitalized interest	(16,788)	(16,763)	(46,499)	(47,854)
Interest expense	$ 16,171	$ 17,092	$ 50,169	$ 51,240