Secured and unsecured senior debt Schedule of interest expense incurred (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Interest expense incurred
Gross interest	$ 36,115	$ 32,680	$ 105,427	$ 92,551
Capitalized interest	(8,436)	(12,125)	(27,844)	(35,440)
Interest	$ 27,679	$ 20,555	$ 77,583	$ 57,111