CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDER'S EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Subsidiaries [Member]	Subsidiaries [Member] Common Stock	Subsidiaries [Member] Additional Paid-in Capital	Subsidiaries [Member] Retained Earnings	Subsidiaries [Member] Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2019	$ 4,000,299		$ 3,308,957	$ 775,491	$ (84,149)	$ 4,048,680	$ 859	$ 3,485,105	$ 751,193	$ (188,477)
Balance (in shares) at Dec. 31, 2019		200					85,903,791
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	182,717			182,717		274,280			274,280
Dividends, Common Stock	(45,421)			(45,421)		(149,072)			(149,072)
Other comprehensive income (loss)	(2,288)				(2,288)	7,521				7,521
Investment from parent	4,575		4,575			0
Balance at Dec. 31, 2020	4,139,882		3,313,532	912,787	(86,437)	4,181,409	$ 859	3,485,105	876,401	(180,956)
Balance (in shares) at Dec. 31, 2020		200					85,903,791
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	260,849			260,849		336,063			336,063
Dividends, Common Stock	(106,420)			(106,420)		(229,857)			(229,857)
Other comprehensive income (loss)	59,005				59,005	67,815				67,815
Investment from parent	210,000		210,000			0
Balance at Dec. 31, 2021	$ 4,563,316		3,523,532	1,067,216	(27,432)	$ 4,355,430	$ 859	3,485,105	982,607	(113,141)
Balance (in shares) at Dec. 31, 2021	200	200				85,903,791	85,903,791
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 414,345			414,345		$ 490,952			490,952
Dividends, Common Stock	(16,230)			(16,230)		(35,396)			(35,396)
Other comprehensive income (loss)	2,658				2,658	10,097				10,097
Investment from parent	0					50,000		50,000
Balance at Dec. 31, 2022	$ 4,964,089		$ 3,523,532	$ 1,465,331	$ (24,774)	$ 4,871,083	$ 859	$ 3,535,105	$ 1,438,163	$ (103,044)
Balance (in shares) at Dec. 31, 2022	200	200				85,903,791	85,903,791