Equity Incentive Awards - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Payment Arrangement [Abstract]
Options forfeited (in shares)		0	0	0
Options expired (in shares)		0	0	0
Shares Subject To Options
Beginning balance (in shares)		41,500	47,100	440,160
Options issued (in shares)	16,090	16,090		12,540
Options exercised (in shares)		0	(5,600)	(405,600)
Ending balance (in shares)		57,590	41,500	47,100	440,160
Exercisable at December 31, 2020 (in shares)		41,500
Weighted Average Exercise Price Per Share
Beginning balance (in usd per share)		$ 40.65	$ 36.95	$ 11.36
Options issued (in usd per share)	$ 66.81	66.81		44.83
Options exercised (in usd per share)			9.43	9.43
Ending balance (in usd per share)		47.96	$ 40.65	$ 36.95	$ 11.36
Exercisable at December 31, 2020 (in usd per share)		$ 40.65
Weighted Average Outstanding Contractual Life (in years)
Balance outstanding, Weighted Average Outstanding Contractual Life (in years)		7 years 2 months 12 days	7 years 3 months 18 days	7 years 3 months 18 days	1 year 7 months 6 days
Exercisable at December 31, 2020 (in years)		6 years 3 months 18 days
Average Intrinsic Value (in millions)
Beginning balance		$ 1.2	$ 0.5	$ 14.6
Options exercised		0.2		16.9
Ending balance		0.9	$ 1.2	$ 0.5	$ 14.6
Exercisable at December 31, 2020		$ 0.9