Equity - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income	$ 32,260	$ 35,489	$ 31,359	$ 19,145	$ 33,008	$ 32,897	$ 24,640	$ 16,705	$ 19,370	$ 26,085	$ 26,585	$ 7,888	$ 118,253	$ 107,250	$ 79,928
Private perpetual preferred unit distributions													(936)	(936)	(936)
Net income attributable to non-controlling interests													(54,670)	(54,858)	(45,262)
Earnings allocated to unvested shares													(36)	(36)	(24)
Net income attributable to common stockholders - basic													62,611	51,420	33,706
Earnings allocated to unvested shares													(36)	(36)	(550)
Net income attributable to common stockholders - diluted													$ 117,281	$ 106,278	$ 78,442
Denominator:
Weighted average shares outstanding - basic (shares)													158,380,000	133,881,000	114,245,000
Operating partnership units (shares)													138,075,000	142,967,000	151,669,000
Effect of dilutive securities, stock-based compensation plans (shares)													775,000	454,000	707,000
Effect of dilutive securities, exchangeable senior notes (shares)													819,000	266,000	0
Weighted average shares outstanding - dilutive (in shares)													298,049,000	277,568,000	266,621,000
Basic (USD per share)													$ 0.40	$ 0.38	$ 0.30
Diluted (USD per share)													$ 0.39	$ 0.38	$ 0.29
Antidilutive securities (shares)													834,267	800,746	0