Secured and unsecured senior debt Schedule of interest expense (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Interest expense incurred
Gross interest	$ 28,735	$ 31,668	$ 59,871	$ 63,709
Capitalized interest	(11,302)	(15,690)	(23,315)	(29,711)
Interest	$ 17,433	$ 15,978	$ 36,556	$ 33,998