Equity - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator - Basic:
Net income	$ 35,489	$ 32,897	$ 85,993	$ 74,242
Private perpetual preferred unit distributions	(234)	(234)	(702)	(702)
Net income attributable to non-controlling interests	(16,449)	(16,690)	(39,916)	(39,050)
Earnings allocated to unvested shares	(11)	(11)	(28)	(27)
Net income attributable to common stockholders - basic	18,795	15,962	45,347	34,463
Numerator - Diluted:
Net income	35,489	32,897	85,993	74,242
Private perpetual preferred unit distributions	(234)	(234)	(702)	(702)
Earnings allocated to unvested shares	(11)	(11)	(28)	(27)
Net income attributable to common stockholders - diluted	$ 35,244	$ 32,652	$ 85,263	$ 73,513
Denominator:
Weighted average shares outstanding - basic (in shares)	158,102,000	136,831,000	157,796,000	126,740,000
Operating partnership units (in shares)	138,287,000	141,908,000	138,593,000	143,648,000
Effect of dilutive securities:
Stock-based compensation plans (in shares)	762,000	1,090,000	848,000	378,000
Exchangeable senior notes (in shares)	720,000	785,000	852,000	262,000
Weighted average shares outstanding - diluted (in shares)	297,871,000	280,614,000	298,089,000	271,028,000
Earnings per share:
Basic (in USD per share)	$ 0.12	$ 0.12	$ 0.29	$ 0.27
Diluted (in USD per share)	$ 0.12	$ 0.12	$ 0.29	$ 0.27
Antidilutive securities (in shares)	954,533	1,033,044	840,092	757,119