Share Incentive Plans - Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation information
Compensation Expense	$ 24,997	$ 30,530	$ 34,607
Compensation Capitalized	1,076	2,726	2,948
Restricted Units In-Lieu of Bonus	1,809	4,022	3,654
Compensation Equity	27,882	37,278	41,209
Dividends Incurred	1,502	14,256	2,779
Restricted Shares [Member]
Compensation information
Compensation Expense	9,209	13,539	13,755
Compensation Capitalized	568	1,477	1,311
Restricted Units In-Lieu of Bonus	0	0	0
Compensation Equity	9,777	15,016	15,066
Dividends Incurred	761	6,494	1,160
Restricted Stock Units (RSUs) [Member]
Compensation information
Compensation Expense	10,214	13,567	17,311
Compensation Capitalized	119	591	538
Restricted Units In-Lieu of Bonus	190	4,022	3,654
Compensation Equity	10,523	18,180	21,503
Dividends Incurred	741	7,762	1,619
Employee Stock Option [Member]
Compensation information
Compensation Expense	4,893	2,839	2,746
Compensation Capitalized	323	593	1,010
Restricted Units In-Lieu of Bonus	1,619	0	0
Compensation Equity	6,835	3,432	3,756
Dividends Incurred	0	0	0
Employee Share Purchase Plan Discount [Member]
Compensation information
Compensation Expense	681	585	795
Compensation Capitalized	66	65	89
Restricted Units In-Lieu of Bonus	0	0	0
Compensation Equity	747	650	884
Dividends Incurred	$ 0	$ 0	$ 0