Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense, Tax Benefit	$ (933)	$ (575)	$ (659)
Share-based Payment Arrangement, Expense, after Tax	2,592	1,597	1,830
Share-based Payment Arrangement, Amount Capitalized	841	430	531
Operations and Maintenance Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	$ 3,525	$ 2,172	$ 2,489

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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