Share and Unit-Based Plans - Compensation cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost under share and unit-based plans	$ 4,616	$ 6,490	$ 28,219	$ 30,437
LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost under share and unit-based plans	3,440	5,269	21,823	24,892
Stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost under share and unit-based plans	972	1,002	5,717	4,947
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost under share and unit-based plans	32	34	94	53
Phantom stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost under share and unit-based plans	$ 172	$ 185	$ 585	$ 545