Summary of Significant Accounting Policies (Details) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) item $ / shares shares	Sep. 30, 2014 USD ($) $ / shares shares
Numerator:
Net income		$ 63,084	$ 33,643	$ 117,944	$ 73,682
Income from consolidated joint ventures attributable to non-controlling interests		(1,982)	(1,803)	(6,643)	(5,704)
Preferred stock dividends		(2,300)	(2,300)	(6,900)	(6,900)
Dividends paid on unvested restricted stock compensation		(49)	(94)	(162)	(291)
Undistributed income allocated to unvested restricted stock compensation		(161)	(119)	(270)	(213)
Numerator for basic and diluted income attributable to common stockholders		$ 58,592	$ 29,327	$ 103,969	$ 60,574
Denominator:
Weighted average basic and diluted common shares outstanding (in shares) | shares		207,604	202,800	207,264	188,901
Basic and diluted income attributable to common stockholders per common share (in dollars per share) | $ / shares		$ 0.28	$ 0.14	$ 0.50	$ 0.32
Segment Reporting
Number of operating segments | item				1
BuyEfficient, LLC | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Denominator:
Goodwill written off due to sale of asset	$ 8,400