Share and Unit-Based Plans - Compensation cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost under share and unit-based plans	$ 6,665	$ 13,612
LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost under share and unit-based plans	3,714	10,108
Stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost under share and unit-based plans	2,660	3,230
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost under share and unit-based plans	51	31
Phantom stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost under share and unit-based plans	$ 240	$ 243