CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDER’S EQUITY Statement - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Subsidiaries [Member]	Subsidiaries [Member] Common Stock [Member]	Subsidiaries [Member] Additional Paid-in Capital [Member]	Subsidiaries [Member] Retained Earnings [Member]	Subsidiaries [Member] AOCI Attributable to Parent [Member]
Beginning Balance (in shares) at Dec. 31, 2018		200					85,903,791
Beginning Balance at Dec. 31, 2018	$ 3,860,758	$ 0	$ 3,308,957	$ 629,003	$ (77,202)	$ 3,707,924	$ 859	$ 3,275,105	$ 622,844	$ (190,884)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	132,154			132,154		147,302			147,302
Common stock dividend paid	(35,994)			(35,994)		(64,604)			(64,604)
Other comprehensive income (loss)	92				92	2,606				2,606
Ending Balance (in shares) at Mar. 31, 2019		200					85,903,791
Ending Balance at Mar. 31, 2019	3,957,010	$ 0	3,308,957	725,163	(77,110)	3,793,228	$ 859	3,275,105	705,542	(188,278)
Beginning Balance (in shares) at Dec. 31, 2018		200					85,903,791
Beginning Balance at Dec. 31, 2018	3,860,758	$ 0	3,308,957	629,003	(77,202)	3,707,924	$ 859	3,275,105	622,844	(190,884)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	99,202					138,977
Other comprehensive income (loss)	183					5,214
Ending Balance (in shares) at Jun. 30, 2019		200					85,903,791
Ending Balance at Jun. 30, 2019	3,924,066	$ 0	3,308,957	692,128	(77,019)	3,768,127	$ 859	3,275,105	677,833	(185,670)
Beginning Balance (in shares) at Mar. 31, 2019		200					85,903,791
Beginning Balance at Mar. 31, 2019	3,957,010	$ 0	3,308,957	725,163	(77,110)	3,793,228	$ 859	3,275,105	705,542	(188,278)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(32,952)			(32,952)		(8,325)			(8,325)
Common stock dividend paid	(83)			(83)		(19,384)			(19,384)
Other comprehensive income (loss)	91				91	2,608				2,608
Ending Balance (in shares) at Jun. 30, 2019		200					85,903,791
Ending Balance at Jun. 30, 2019	$ 3,924,066	$ 0	3,308,957	692,128	(77,019)	$ 3,768,127	$ 859	3,275,105	677,833	(185,670)
Beginning Balance (in shares) at Dec. 31, 2019	200	200				85,903,791	85,903,791
Beginning Balance at Dec. 31, 2019	$ 4,000,299	$ 0	3,308,957	775,491	(84,149)	$ 4,048,680	$ 859	3,485,105	751,193	(188,477)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	94,936			94,936		111,321			111,321
Common stock dividend paid	(22,645)			(22,645)		(53,794)			(53,794)
Other comprehensive income (loss)	5,170				5,170	7,806				7,806
Ending Balance (in shares) at Mar. 31, 2020		200					85,903,791
Ending Balance at Mar. 31, 2020	$ 4,077,760	$ 0	3,308,957	847,782	(78,979)	$ 4,114,013	$ 859	3,485,105	808,720	(180,671)
Beginning Balance (in shares) at Dec. 31, 2019	200	200				85,903,791	85,903,791
Beginning Balance at Dec. 31, 2019	$ 4,000,299	$ 0	3,308,957	775,491	(84,149)	$ 4,048,680	$ 859	3,485,105	751,193	(188,477)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	71,703					126,358
Other comprehensive income (loss)	$ 6,800					$ 11,762
Ending Balance (in shares) at Jun. 30, 2020	200	200				85,903,791	85,903,791
Ending Balance at Jun. 30, 2020	$ 4,033,738	$ 0	3,308,957	802,130	(77,349)	$ 4,086,991	$ 859	3,485,105	777,742	(176,715)
Beginning Balance (in shares) at Mar. 31, 2020		200					85,903,791
Beginning Balance at Mar. 31, 2020	4,077,760	$ 0	3,308,957	847,782	(78,979)	4,114,013	$ 859	3,485,105	808,720	(180,671)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(23,233)			(23,233)		15,037			15,037
Common stock dividend paid	(22,419)			(22,419)		(46,015)			(46,015)
Other comprehensive income (loss)	$ 1,630				1,630	$ 3,956				3,956
Ending Balance (in shares) at Jun. 30, 2020	200	200				85,903,791	85,903,791
Ending Balance at Jun. 30, 2020	$ 4,033,738	$ 0	$ 3,308,957	$ 802,130	$ (77,349)	$ 4,086,991	$ 859	$ 3,485,105	$ 777,742	$ (176,715)