Other Assets - Summary of Other Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Other Assets Noncurrent [Abstract]
Deferred financing costs on undrawn revolver, Gross Carrying Amount	$ 967	$ 967
Other regulatory assets Deferred financing costs, Gross Carrying Amount	27,761	27,761
Other regulatory assets Deferred costs recoverable in future years, Gross Carrying Amount	23,793	23,793
Other regulatory assets, Gross Carrying Amount	51,554	51,554
Investments, Gross Carrying Amount	2,519	2,519
Other assets, Gross Carrying Amount	55,040	55,040
Deferred financing costs on undrawn revolver, Accumulated Amortization	(446)	(397)
Other regulatory assets Deferred financing costs, Accumulated Amortization	(17,944)	(16,997)
Other regulatory assets, Accumulated Amortization	(17,944)	(16,997)
Other assets, Accumulated Amortization	(18,390)	(17,394)
Deferred financing costs on undrawn revolver, Net Carrying Amount	521	570
Other regulatory assets Deferred financing costs, Net Carrying Amount	9,817	10,764
Other regulatory assets Deferred costs recoverable in future years, Net Carrying Amount	23,793	23,793
Other regulatory assets, Net Carrying Amount	33,610	34,557
Investments, Net Carrying Amount	2,519	2,519
Other assets, Net Carrying Amount	$ 36,650	$ 37,646