Equity - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator - Basic:
Net income	$ 18,930	$ 30,184	$ 28,786	$ 48,242
Private perpetual preferred unit distributions	(234)	(234)	(468)	(468)
Net income attributable to non-controlling interests	(7,609)	(13,299)	(11,554)	(21,355)
Earnings allocated to unvested shares	(13)	(10)	(20)	(16)
Net income attributable to common stockholders - basic	11,074	16,641	16,744	26,403
Numerator - Diluted:
Net income	18,930	30,184	28,786	48,242
Private perpetual preferred unit distributions	(234)	(234)	(468)	(468)
Earnings allocated to unvested shares	(13)	(10)	(20)	(16)
Net income attributable to common stockholders - diluted	$ 18,683	$ 29,940	$ 28,298	$ 47,758
Denominator:
Weighted average shares outstanding - basic (in shares)	176,796,000	165,256,000	176,495,000	164,311,000
Operating partnership units (in shares)	121,335,000	131,988,000	121,605,000	132,717,000
Effect of dilutive securities:
Stock-based compensation plans (in shares)	0	0	0	1,000
Weighted average shares outstanding - diluted (in shares)	298,131,000	297,244,000	298,100,000	297,029,000
Earnings per share:
Basic (in USD per share)	$ 0.06	$ 0.10	$ 0.09	$ 0.16
Diluted (in USD per share)	$ 0.06	$ 0.10	$ 0.09	$ 0.16
Antidilutive securities (in shares)	411,019	414,801	205,851	417,074