Accounts payable, accrued expenses, and tenant security deposits (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Payables and Accruals [Abstract]
Accounts payable and accrued expenses	$ 98,037	$ 105,520
Accrued construction	78,098	83,104
Acquired below market leases	11,405	14,721
Conditional asset retirement obligations	7,386	9,240
Deferred rent liability	35,134	34,414
Interest rate swap liabilities	6,191	20,661
Prepaid rent and tenant security deposits	188,241	143,878
Other liabilities	10,850	12,170
Total	$ 435,342	$ 423,708