CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Cumulative Earnings	Cumulative Distributions to Stockholders
Beginning balance (in shares) at Dec. 31, 2018		84,884,344
Balance at beginning of period at Dec. 31, 2018	$ 1,348,794	$ 849	$ 1,811,422	$ 61,297	$ 1,409,941	$ (1,934,715)
Increase (Decrease) in Stockholders' Equity
Net Income (Loss)	85,730				85,730
Other comprehensive income (loss)	(12,374)			(12,374)
Issuance of common stock (in shares)		12,291,191
Issuance of common stock	190,108	$ 123	189,985
Direct stock purchase and dividend reinvestment plan (in shares)		399,838
Direct stock purchase and dividend reinvestment plan	6,307	$ 4	6,303
Employee stock purchase and incentive plans (in shares)		139,648
Employee stock purchase and incentive plans	(1,920)	$ 1	(1,921)
Non-cash equity award compensation	7,255		7,255
Common dividends declared	(59,868)					(59,868)
Ending balance (in shares) at Jun. 30, 2019		97,715,021
Balance at End of Period at Jun. 30, 2019	1,564,032	$ 977	2,013,044	48,923	1,495,671	(1,994,583)
Beginning balance (in shares) at Mar. 31, 2019		96,866,464
Balance at beginning of period at Mar. 31, 2019	1,549,927	$ 969	1,996,358	52,684	1,464,405	(1,964,489)
Increase (Decrease) in Stockholders' Equity
Net Income (Loss)	31,266				31,266
Other comprehensive income (loss)	(3,761)			(3,761)
Issuance of common stock (in shares)		791,191
Issuance of common stock	12,511	$ 8	12,503
Employee stock purchase and incentive plans (in shares)		57,366
Employee stock purchase and incentive plans	18		18
Non-cash equity award compensation	4,165		4,165
Common dividends declared	(30,094)					(30,094)
Ending balance (in shares) at Jun. 30, 2019		97,715,021
Balance at End of Period at Jun. 30, 2019	1,564,032	$ 977	2,013,044	48,923	1,495,671	(1,994,583)
Beginning balance (in shares) at Dec. 31, 2019		114,353,036
Balance at beginning of period at Dec. 31, 2019	1,827,231	$ 1,144	2,269,617	41,513	1,579,124	(2,064,167)
Increase (Decrease) in Stockholders' Equity
Net Income (Loss)	(777,954)				(777,954)
Other comprehensive income (loss)	(70,904)			(70,904)
Issuance of common stock (in shares)		350,088
Issuance of common stock	5,547	$ 3	5,544
Employee stock purchase and incentive plans (in shares)		237,073
Employee stock purchase and incentive plans	(2,774)	$ 2	(2,776)
Non-cash equity award compensation	7,240		7,240
Common dividends declared	(51,810)					(51,810)
Ending balance (in shares) at Jun. 30, 2020		114,940,197
Balance at End of Period at Jun. 30, 2020	936,576	$ 1,149	2,279,625	(29,391)	801,170	(2,115,977)
Beginning balance (in shares) at Mar. 31, 2020		114,837,533
Balance at beginning of period at Mar. 31, 2020	725,202	$ 1,148	2,275,808	(85,531)	635,726	(2,101,949)
Increase (Decrease) in Stockholders' Equity
Net Income (Loss)	165,444				165,444
Other comprehensive income (loss)	56,140			56,140
Direct stock purchase and dividend reinvestment plan (in shares)		0
Employee stock purchase and incentive plans (in shares)		102,664
Employee stock purchase and incentive plans	(234)	$ 1	(235)
Non-cash equity award compensation	4,052		4,052
Common dividends declared	(14,028)					(14,028)
Ending balance (in shares) at Jun. 30, 2020		114,940,197
Balance at End of Period at Jun. 30, 2020	$ 936,576	$ 1,149	$ 2,279,625	$ (29,391)	$ 801,170	$ (2,115,977)