Schedule I - Condensed Financial Information Of Registrant (Unconsolidated Statements Of Common Shareholders' Equity (Deficit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Other Comprehensive Income (Loss), Net of Tax		$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 573,266	572,276	571,183
Net income applicable to common stock	129,180	130,812	105,580
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	109,430	130,812	105,580
Distributions to AES	(136,426)	(130,179)	(105,144)
Other	206	357	657
Ending Balance	546,476	573,266	572,276
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Other Comprehensive Income (Loss), Net of Tax	(19,750)	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	573,266	572,276	571,183
Net income applicable to common stock	129,180	130,812	105,580
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	109,430	130,812	105,580
Distributions to AES	136,426	130,179	105,144
Other	206	357	657
Ending Balance	546,476	573,266	572,276
Paid In Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	597,824	597,467	596,810
Return of Capital	(7,246)
Other	206	357	657
Ending Balance	590,784	597,824	597,467
Paid In Capital [Member] | Parent Company [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	597,824	597,467	596,810
Return of Capital	(7,246)
Other	206	357	657
Ending Balance	590,784	597,824	597,467
AOCI Attributable to Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Other Comprehensive Income (Loss), Net of Tax	(19,750)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Ending Balance	(19,750)
AOCI Attributable to Parent [Member] | Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Other Comprehensive Income (Loss), Net of Tax	(19,750)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Ending Balance	(19,750)
Accumulated Deficit [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(24,558)	(25,191)	(25,627)
Net income applicable to common stock	129,180	130,812	105,580
Distributions to AES	(129,180)	(130,179)	(105,144)
Ending Balance	(24,558)	(24,558)	(25,191)
Accumulated Deficit [Member] | Parent Company [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(24,558)	(25,191)	(25,627)
Net income applicable to common stock	129,180	130,812	105,580
Distributions to AES	129,180	130,179	105,144
Ending Balance	$ (24,558)	$ (24,558)	$ (25,191)