Share Based Payments (Summary of share based compensation expense and unearned compensation) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Expense	$ 9,286	$ 10,803	$ 11,436	$ 9,286
Unearned Compensation		6,668	6,545
LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Expense		5,646	4,120	2,486
Unearned Compensation		2,878	3,027
Restricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Expense		1,495	1,443	1,033
Unearned Compensation		1,051	1,318
Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Expense		680	680	593
Unearned Compensation		0	0
Market Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Expense		1,467	1,120	1,002
Unearned Compensation		2,739	2,200
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Expense		1,515	4,073	$ 4,172
Unearned Compensation		$ 0	$ 0