Noncontrolling Interests Redeemable interest in property partnerships (narrative) (Details) - USD ($) $ in Thousands				12 Months Ended
	Sep. 15, 2015	Aug. 06, 2015	Oct. 04, 2012	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Payments for Repurchase of Redeemable Noncontrolling Interest				$ 0	$ 108,499	$ 0
Fountain Square
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Aggregate purchase price			$ 385,000
Debt recorded upon consolidation			$ 211,300
Ownership Percentage	50.00%	50.00%	50.00%
Fixed Price to Acquire Remaining Portion of Joint venture		$ 100,900
Consideration paid			$ 87,000
Ownership Percentage by Parent			50.00%
Future Fixed Price to Acquire Remaining Portion of Joint venture			$ 102,000
Payments for Repurchase of Redeemable Noncontrolling Interest	$ 100,900
Mortgage debt assumed upon acquisition of noncontrolling interest	$ 105,600