Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Balance, beginning of period at Dec. 31, 2020	$ 1,304,953	$ 66,876	$ 1,674,576	$ (315,510)	$ (120,989)
Balance, beginning of period (shares) at Dec. 31, 2020		66,876,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	131,106			131,106
Shares issued for stock compensation		$ 166	(166)
Shares issued for stock compensation (shares)		166,000
Equity-based compensation expense	1,930		1,930
Pension plans and OPEB obligations, net of tax	2,953				2,953
Cash flow hedges, net of tax	64,107				64,107
Dividends on common stock	(27,484)			(27,484)
Other transactions, net	(16)		81	(97)
Balance, end of period at Mar. 31, 2021	1,477,549	$ 67,042	1,676,421	(211,985)	(53,929)
Balance, end of period (shares) at Mar. 31, 2021		67,042,000
Balance, beginning of period at Dec. 31, 2020	1,304,953	$ 66,876	1,674,576	(315,510)	(120,989)
Balance, beginning of period (shares) at Dec. 31, 2020		66,876,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 319,011
Repurchase of common stock (shares)	0
Cash flow hedges, net of tax	$ 32,944
Balance, end of period at Jun. 30, 2021	1,611,789	$ 67,045	1,678,661	(51,670)	(82,247)
Balance, end of period (shares) at Jun. 30, 2021		67,045,000
Balance, beginning of period at Mar. 31, 2021	1,477,549	$ 67,042	1,676,421	(211,985)	(53,929)
Balance, beginning of period (shares) at Mar. 31, 2021		67,042,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	187,905			187,905
Shares issued for stock compensation		$ 3	(3)
Shares issued for stock compensation (shares)		3,000
Equity-based compensation expense	2,140		2,140
Pension plans and OPEB obligations, net of tax	2,845				2,845
Cash flow hedges, net of tax	(31,163)				(31,163)
Dividends on common stock	(27,489)			(27,489)
Other transactions, net	2		103	(101)
Balance, end of period at Jun. 30, 2021	1,611,789	$ 67,045	1,678,661	(51,670)	(82,247)
Balance, end of period (shares) at Jun. 30, 2021		67,045,000
Balance, beginning of period at Dec. 31, 2021	$ 1,526,133	$ 69,064	1,781,217	(280,910)	(43,238)
Balance, beginning of period (shares) at Dec. 31, 2021	69,064,000	69,064,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 163,880			163,880
Shares issued for stock compensation		$ 308	(308)
Shares issued for stock compensation (shares)		308,000
Equity-based compensation expense	2,056		2,056
Pension plans and OPEB obligations, net of tax	7,480				7,480
Cash flow hedges, net of tax	43,276				43,276
Dividends on common stock	(30,524)			(30,524)
Other transactions, net	(103)		(25)	(78)
Balance, end of period at Mar. 31, 2022	1,712,198	$ 69,372	1,782,940	(147,632)	7,518
Balance, end of period (shares) at Mar. 31, 2022		69,372,000
Balance, beginning of period at Dec. 31, 2021	$ 1,526,133	$ 69,064	1,781,217	(280,910)	(43,238)
Balance, beginning of period (shares) at Dec. 31, 2021	69,064,000	69,064,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 284,102
Repurchase of common stock	$ (4,200)
Repurchase of common stock (shares)	(94,566)
Cash flow hedges, net of tax	$ 85,805
Balance, end of period at Jun. 30, 2022	$ 1,843,551	$ 69,280	1,785,383	(62,074)	50,962
Balance, end of period (shares) at Jun. 30, 2022	69,280,000	69,280,000
Balance, beginning of period at Mar. 31, 2022	$ 1,712,198	$ 69,372	1,782,940	(147,632)	7,518
Balance, beginning of period (shares) at Mar. 31, 2022		69,372,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	120,222			120,222
Shares issued for stock compensation		$ 3	(3)
Shares issued for stock compensation (shares)		3,000
Equity-based compensation expense	2,368		2,368
Repurchase of common stock	(4,156)	$ (95)		(4,061)
Repurchase of common stock (shares)		(95,000)
Pension plans and OPEB obligations, net of tax	915				915
Cash flow hedges, net of tax	42,529				42,529
Dividends on common stock	(30,524)			(30,524)
Other transactions, net	(1)		78	(79)
Balance, end of period at Jun. 30, 2022	$ 1,843,551	$ 69,280	$ 1,785,383	$ (62,074)	$ 50,962
Balance, end of period (shares) at Jun. 30, 2022	69,280,000	69,280,000