Stock-based Compensation (Summary of Unrecognized Compensation Expense) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 24,914
Unrecognized compensation expense, Weighted Average Remaining Contractual Term	1 year 219 days
Out Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 17,930
Unrecognized compensation expense, Weighted Average Remaining Contractual Term	1 year 219 days
Out Performance Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 3,798
Unrecognized compensation expense, Weighted Average Remaining Contractual Term	1 year 292 days
AO LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 1,371
Unrecognized compensation expense, Weighted Average Remaining Contractual Term	1 year 219 days
Employee Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 902
Unrecognized compensation expense, Weighted Average Remaining Contractual Term	1 year 255 days
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 913
Unrecognized compensation expense, Weighted Average Remaining Contractual Term	1 year 255 days