Equity - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator - Basic:
Net income	$ 29,230	$ 35,489	$ 77,472	$ 85,993
Private perpetual preferred unit distributions	(234)	(234)	(702)	(702)
Net income attributable to non-controlling interests	(12,654)	(16,449)	(34,009)	(39,916)
Earnings allocated to unvested shares	(10)	(11)	(26)	(28)
Net income attributable to common stockholders - basic	16,332	18,795	42,735	45,347
Numerator - Diluted:
Net income	29,230	35,489	77,472	85,993
Private perpetual preferred unit distributions	(234)	(234)	(702)	(702)
Earnings allocated to unvested shares	(10)	(11)	(26)	(28)
Net income attributable to common stockholders - diluted	$ 28,986	$ 35,244	$ 76,744	$ 85,263
Denominator:
Weighted average shares outstanding - basic (in shares)	167,657,000	158,102,000	165,613,000	157,796,000
Operating partnership units (in shares)	129,821,000	138,287,000	131,567,000	138,593,000
Effect of dilutive securities:
Stock-based compensation plans (in shares)	0	762,000	1,000	848,000
Exchangeable senior notes (in shares)	0	720,000	0	852,000
Weighted average shares outstanding - diluted (in shares)	297,478,000	297,871,000	297,181,000	298,089,000
Earnings per share:
Basic (in USD per share)	$ 0.10	$ 0.12	$ 0.26	$ 0.29
Diluted (in USD per share)	$ 0.10	$ 0.12	$ 0.26	$ 0.29
Antidilutive securities (in shares)	541,947	954,533	458,698	840,092