Nature of Operations and Basis of Consolidation (Details) $ in Thousands	Mar. 31, 2018 USD ($) watts	Dec. 31, 2017 USD ($) customers
Reclassification of certain tax effects from AOCL	$ (2,143)	$ 0
Number of customers | customers		718,300
Number of megawatts of qualifying facility | watts	35
Estimated aggregate gross contractual payments for qualifying facilities through 2024	$ 212,700
Restatement Adjustment [Member]
Reclassification of certain tax effects from AOCL	$ 2,100