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, 2019		200					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) Attributable to Parent	94,936			94,936		111,321			111,321
Dividends, Common Stock	(22,645)			(22,645)		(53,794)			(53,794)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	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, 2020		200				85,903,791	85,903,791
Beginning Balance at Dec. 31, 2020	4,139,882	$ 0	3,313,532	912,787	(86,437)	$ 4,181,409	$ 859	3,485,105	876,401	(180,956)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	188,993			188,993		199,470			199,470
Dividends, Common Stock	(22,939)			(22,939)		(52,053)			(52,053)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	$ 2,385				2,385	$ 4,554				4,554
Ending Balance (in shares) at Mar. 31, 2021	200	200				85,903,791	85,903,791
Ending Balance at Mar. 31, 2021	$ 4,308,321	$ 0	$ 3,313,532	$ 1,078,841	$ (84,052)	$ 4,333,380	$ 859	$ 3,485,105	$ 1,023,818	$ (176,402)