Stockholders' Equity - Computation of basic and diluted earnings (loss) per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Weighted average Common Shares outstanding
Weighted average common shares outstanding	135,367,081	129,228,102	135,062,708	127,577,389
Non-vested shares	(1,733,435)	(1,778,648)	(1,727,762)	(1,778,674)
Weighted average common shares outstanding - basic	133,633,646	127,449,454	133,334,946	125,798,715
Dilutive effect of forward equity shares	0	0	2,149	0
Dilutive effect of employee stock purchase plan	62,266	75,153	83,217	90,640
Weighted average Common Shares outstanding—Diluted	133,695,912	127,524,607	133,420,312	125,889,355
Net Income	$ 75,513	$ 4,484	$ 79,828	$ 9,375
Dividends paid on nonvested share-based awards	(521)	(534)	(1,039)	(1,070)
Net income applicable to common stockholders	$ 74,992	$ 3,950	$ 78,789	$ 8,305
Basic earnings per common share (in dollars per share)	$ 0.56	$ 0.03	$ 0.59	$ 0.07
Diluted earnings per common share (in dollars per share)	$ 0.56	$ 0.03	$ 0.59	$ 0.07