Other Assets - Summary of Other Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Other Assets Noncurrent [Abstract]
Deferred financing costs on undrawn revolver, Gross Carrying Amount	$ 1,025	$ 1,025
Other regulatory assets Deferred financing costs, Gross Carrying Amount	10,610	10,610
Other regulatory assets Deferred costs recoverable in future years, Gross Carrying Amount	23,793	23,793
Other regulatory assets, Gross Carrying Amount	34,403	34,403
Operating lease right-of-use asset, Gross Carrying Amount	345
Investments, Gross Carrying Amount	2,519	2,519
Other assets, Gross Carrying Amount	38,292	37,947
Deferred financing costs on undrawn revolver, Accumulated Amortization	(811)	(779)
Other regulatory assets Deferred financing costs, Accumulated Amortization	(5,810)	(5,490)
Other regulatory assets, Accumulated Amortization	(5,810)	(5,490)
Other assets, Accumulated Amortization	(6,621)	(6,269)
Deferred financing costs on undrawn revolver, Net Carrying Amount	214	246
Other regulatory assets Deferred financing costs, Net Carrying Amount	4,800	5,120
Other regulatory assets Deferred costs recoverable in future years, Net Carrying Amount	23,793	23,793
Other regulatory assets, Net Carrying Amount	28,593	28,913
Operating lease right-of-use asset, Net Carrying Amount	345
Investments, Net Carrying Amount	2,519	2,519
Other assets, Net Carrying Amount	$ 31,671	$ 31,678