Stockholders' Equity - Computation of basic and diluted earnings (loss) per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Weighted average Common Shares outstanding
Weighted average common shares outstanding (in shares)	136,048,781	129,865,985	135,393,798	128,348,638
Non-vested shares	(1,739,364)	(1,775,911)	(1,731,658)	(1,777,743)
Weighted average common shares outstanding - basic (in shares)	134,309,417	128,090,074	133,662,140	126,570,895
Dilutive effect of forward equity shares (in shares)	0	0	0	0
Dilutive effect of employee stock purchase plan (in shares)	47,810	78,610	74,029	85,690
Weighted average common shares outstanding - diluted (in shares)	134,357,227	128,168,684	133,736,169	126,656,585
Net Income	$ 8,230	$ 2,601	$ 88,058	$ 11,975
Dividends paid on nonvested share-based awards	(522)	(534)	(1,561)	(1,603)
Net income applicable to common stockholders	$ 7,708	$ 2,067	$ 86,497	$ 10,372
Basic earnings per common share (in dollars per share)	$ 0.06	$ 0.02	$ 0.65	$ 0.08
Diluted earnings per common share (in dollars per share)	$ 0.06	$ 0.02	$ 0.65	$ 0.08