Equity - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator - Basic:
Net income	$ 26,784	$ 29,230	$ 55,570	$ 77,472
Private perpetual preferred unit distributions	(234)	(234)	(702)	(702)
Net income attributable to non-controlling interests	(10,668)	(12,654)	(22,222)	(34,009)
Earnings allocated to unvested shares	(13)	(10)	(33)	(26)
Net income attributable to common stockholders - basic	15,869	16,332	32,613	42,735
Numerator - Diluted:
Net income	26,784	29,230	55,570	77,472
Private perpetual preferred unit distributions	(234)	(234)	(702)	(702)
Earnings allocated to unvested shares	(13)	(10)	(33)	(26)
Net income attributable to common stockholders - diluted	$ 26,537	$ 28,986	$ 54,835	$ 76,744
Denominator:
Weighted average shares outstanding - basic (in shares)	178,352,000	167,657,000	177,428,000	165,613,000
Operating partnership units (in shares)	119,799,000	129,821,000	120,689,000	131,567,000
Effect of dilutive securities:
Stock-based compensation plans (in shares)	0	0	0	1,000
Weighted average shares outstanding - diluted (in shares)	298,151,000	297,478,000	298,117,000	297,181,000
Earnings per share:
Basic (in USD per share)	$ 0.09	$ 0.10	$ 0.18	$ 0.26
Diluted (in USD per share)	$ 0.09	$ 0.10	$ 0.18	$ 0.26
Antidilutive securities (in shares)	452,457	541,947	288,053	458,698