Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income	$ 51,262	$ 51,415	$ 89,717	$ 115,242
Income from consolidated joint venture attributable to noncontrolling interest	(2,374)	(2,183)	(4,813)	(4,175)
Preferred stock dividends	(3,207)	(3,207)	(6,414)	(6,414)
Numerator for basic and diluted income attributable to common stockholders	$ 45,443	$ 45,777	$ 78,074	$ 104,096
Denominator:
Weighted average basic and diluted common shares outstanding (in shares)	225,232	220,130	224,760	219,614
Basic and diluted income attributable to common stockholders per common share (in dollars per share)	$ 0.20	$ 0.21	$ 0.35	$ 0.47
Restricted Shares
Numerator:
Distributions paid on unvested restricted stock compensation	$ (59)	$ (60)	$ (118)	$ (120)
Undistributed income allocated to unvested restricted stock compensation	$ (179)	$ (188)	$ (298)	$ (437)