Summary of Significant Accounting Policies - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Allowance as of the beginning of the year		$ 2,419	$ 5,233	$ 5,132
Additions expensed during the year	[1]	11,280	460	3,917
Net deductions		(2,312)	(3,274)	(3,816)
Allowance as of the end of the year		$ 11,387	$ 2,419	$ 5,233

[1] Increase in 2020 related to COVID-19, bad debt expense in excess of the amount recovered through rates of $7.1 million, was deferred as a regulatory asset.