CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Shares	Cumulative Common Distributions	Additional Paid in Capital	Cumulative Net Income Available for Common Shareholders	Cumulative Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2018		164,441,709
Beginning balance at Dec. 31, 2018	$ 2,597,431	$ 1,644	$ (5,181,323)	$ 4,545,481	$ 3,231,895	$ (266)
Increase (Decrease) in Shareholders' Equity
Net income (loss)	225,787				225,787
Equity interest in investee’s unrealized gains (losses)	66					66
Common share grants	436			436
Distributions	(87,154)		(87,154)
Ending balance (in shares) at Mar. 31, 2019		164,441,709
Ending balance at Mar. 31, 2019	2,736,566	$ 1,644	(5,268,477)	4,545,917	3,457,682	(200)
Beginning balance (in shares) at Dec. 31, 2018		164,441,709
Beginning balance at Dec. 31, 2018	2,597,431	$ 1,644	(5,181,323)	4,545,481	3,231,895	(266)
Increase (Decrease) in Shareholders' Equity
Net income (loss)	274,643
Equity interest in investee’s unrealized gains (losses)	91
Ending balance (in shares) at Sep. 30, 2019		164,565,303
Ending balance at Sep. 30, 2019	2,608,986	$ 1,646	(5,446,078)	4,547,055	3,506,538	(175)
Beginning balance (in shares) at Mar. 31, 2019		164,441,709
Beginning balance at Mar. 31, 2019	2,736,566	$ 1,644	(5,268,477)	4,545,917	3,457,682	(200)
Increase (Decrease) in Shareholders' Equity
Net income (loss)	8,782				8,782
Equity interest in investee’s unrealized gains (losses)	71					71
Common share grants (in shares)		15,000
Common share grants	869	$ 1		868
Common share repurchases (in shares)		(2,172)
Common share repurchases	(48)			(48)
Distributions	(88,798)		(88,798)
Ending balance (in shares) at Jun. 30, 2019		164,454,537
Ending balance at Jun. 30, 2019	2,657,442	$ 1,645	(5,357,275)	4,546,737	3,466,464	(129)
Increase (Decrease) in Shareholders' Equity
Net income (loss)	40,074				40,074
Equity interest in investee’s unrealized gains (losses)	(46)					(46)
Common share grants (in shares)		140,100
Common share grants	1,068	$ 1		1,067
Common share repurchases (in shares)		(29,334)
Common share repurchases	(749)			(749)
Distributions	(88,803)		(88,803)
Ending balance (in shares) at Sep. 30, 2019		164,565,303
Ending balance at Sep. 30, 2019	2,608,986	$ 1,646	(5,446,078)	4,547,055	3,506,538	(175)
Beginning balance (in shares) at Dec. 31, 2019		164,563,034
Beginning balance at Dec. 31, 2019	2,505,878	$ 1,646	(5,534,942)	4,547,529	3,491,645	0
Increase (Decrease) in Shareholders' Equity
Net income (loss)	(33,650)				(33,650)
Common share grants (in shares)		6,000
Common share grants	$ 590			590
Common share repurchases (in shares)	(2,637)	(2,637)
Common share repurchases	$ (43)			(43)
Distributions	(90,509)		(90,509)
Ending balance (in shares) at Mar. 31, 2020		164,566,397
Ending balance at Mar. 31, 2020	2,382,266	$ 1,646	(5,625,451)	4,548,076	3,457,995	0
Beginning balance (in shares) at Dec. 31, 2019		164,563,034
Beginning balance at Dec. 31, 2019	2,505,878	$ 1,646	(5,534,942)	4,547,529	3,491,645	0
Increase (Decrease) in Shareholders' Equity
Net income (loss)	(173,641)
Equity interest in investee’s unrealized gains (losses)	63
Ending balance (in shares) at Sep. 30, 2020		164,823,833
Ending balance at Sep. 30, 2020	2,242,084	$ 1,648	(5,627,097)	4,549,466	3,318,004	63
Beginning balance (in shares) at Mar. 31, 2020		164,566,397
Beginning balance at Mar. 31, 2020	2,382,266	$ 1,646	(5,625,451)	4,548,076	3,457,995	0
Increase (Decrease) in Shareholders' Equity
Net income (loss)	(37,349)				(37,349)
Common share grants (in shares)		35,000
Common share grants	$ 831			831
Common share repurchases (in shares)	(3,808)
Common share repurchases and forfeitures (in shares)		(3,808)
Common share repurchases and forfeitures	$ (27)			(27)
Ending balance (in shares) at Jun. 30, 2020		164,597,589
Ending balance at Jun. 30, 2020	2,345,721	$ 1,646	(5,625,451)	4,548,880	3,420,646	0
Increase (Decrease) in Shareholders' Equity
Net income (loss)	(102,642)				(102,642)
Equity interest in investee’s unrealized gains (losses)	63					63
Common share grants (in shares)		264,400
Common share grants	871	$ 3		868
Common share repurchases and forfeitures (in shares)		(38,156)
Common share repurchases and forfeitures	(283)	$ (1)		(282)
Distributions	(1,646)		(1,646)
Ending balance (in shares) at Sep. 30, 2020		164,823,833
Ending balance at Sep. 30, 2020	$ 2,242,084	$ 1,648	$ (5,627,097)	$ 4,549,466	$ 3,318,004	$ 63