Schedule I - Condensed Financial Information Of Registrant (Unconsolidated Statements Of Common Shareholders' Equity (Deficit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Other Comprehensive Income (Loss), Net of Tax	$ 14,013	$ (23,670)	$ (19,750)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	520,988	546,476	573,266
Net income applicable to common stock	115,969	106,754	129,180
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	129,982	83,084	109,430
Distributions to AES	(131,476)	(108,739)	(136,426)
Proceeds from Contributed Capital	275,000	0	0
Other	106	167	206
Ending Balance	794,600	520,988	546,476
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Other Comprehensive Income (Loss), Net of Tax	14,013	(23,670)	(19,750)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	520,988	546,476	573,266
Net income applicable to common stock	115,969	106,754	129,180
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	129,982	83,084	109,430
Distributions to AES	131,476	108,739	136,426
Proceeds from Contributed Capital	275,000	0	0
Other	106	167	206
Ending Balance	794,600	520,988	546,476
Paid In Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	588,966	590,784	597,824
Return of Capital	(15,507)	(1,985)	(7,246)
Proceeds from Contributed Capital	275,000
Other	106	167	206
Ending Balance	848,565	588,966	590,784
Paid In Capital [Member] | Parent Company [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	588,966	590,784	597,824
Return of Capital	(15,507)	(1,985)	(7,246)
Proceeds from Contributed Capital	275,000
Other	106	167	206
Ending Balance	848,565	588,966	590,784
AOCI Attributable to Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Other Comprehensive Income (Loss), Net of Tax	14,013	(23,670)	(19,750)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(43,420)	(19,750)
Ending Balance	(29,407)	(43,420)	(19,750)
AOCI Attributable to Parent [Member] | Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Other Comprehensive Income (Loss), Net of Tax	14,013	(23,670)	(19,750)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(43,420)	(19,750)
Ending Balance	(29,407)	(43,420)	(19,750)
Accumulated Deficit [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(24,558)	(24,558)	(24,558)
Net income applicable to common stock	115,969	106,754	129,180
Distributions to AES	(115,969)	(106,754)	(129,180)
Ending Balance	(24,558)	(24,558)	(24,558)
Accumulated Deficit [Member] | Parent Company [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(24,558)	(24,558)	(24,558)
Net income applicable to common stock	115,969	106,754	129,180
Distributions to AES	115,969	106,754	129,180
Ending Balance	$ (24,558)	$ (24,558)	$ (24,558)