Equity - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator:
Net income	$ 24,640	$ 26,585	$ 41,345	$ 34,473
Private perpetual preferred unit distributions	(234)	(234)	(468)	(468)
Net income attributable to non-controlling interests	(13,317)	(15,231)	(22,360)	(19,747)
Earnings allocated to unvested shares	(10)	(7)	(18)	(13)
Net income attributable to common stockholders - basic	11,079	11,113	18,499	14,245
Earnings allocated to unvested shares and LTIP units	(215)	(161)	(387)	(284)
Net income attributable to common stockholders - diluted	$ 24,191	$ 26,190	$ 40,490	$ 33,721
Denominator:
Weighted average shares outstanding - basic (in shares)	122,502,000	112,852,000	121,640,000	111,136,000
Operating partnership units (in shares)	143,665,000	153,015,000	144,511,000	154,730,000
Stock-based compensation plans (in shares)	0	0	970,000	0
Weighted average shares outstanding - diluted (in shares)	266,167,000	265,867,000	267,121,000	265,866,000
Basic (in USD per share)	$ 0.09	$ 0.10	$ 0.15	$ 0.13
Diluted (in USD per share)	$ 0.09	$ 0.10	$ 0.15	$ 0.13
Antidilutive securities (in shares)	1,069,803	744,007	0	628,935