Equity - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator - Basic:
Net income	$ 18,058	$ 19,145
Private perpetual preferred unit distributions	(234)	(234)
Net income attributable to non-controlling interests	(8,056)	(8,926)
Earnings allocated to unvested shares	(6)	(7)
Net income attributable to common stockholders - basic	9,762	9,978
Numerator - Diluted:
Net income	18,058	19,145
Private perpetual preferred unit distributions	(234)	(234)
Earnings allocated to unvested shares	(6)	(7)
Net income attributable to common stockholders - diluted	$ 17,818	$ 18,904
Denominator:
Weighted average shares outstanding - basic (in shares)	162,667,000	156,493,000
Operating partnership units (in shares)	134,157,000	139,895,000
Effect of dilutive securities:
Stock-based compensation plans (in shares)	3,000	775,000
Exchangeable senior notes (in shares)	0	799,000
Weighted average shares outstanding - diluted (in shares)	296,827,000	297,962,000
Earnings per share:
Basic (in USD per share)	$ 0.06	$ 0.06
Diluted (in USD per share)	$ 0.06	$ 0.06
Antidilutive securities (in shares)	419,347	622,565