Retirement Savings Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Savings Plan
Maximum contribution by participants (as a percent)	60.00%
Employer matching contributions (as a percent)	50.00%
Maximum percentage of employees' gross pay subject to employer matching contributions	4.00%
Benefit expense for the 401(k) Plan	$ 0.3	$ 0.3	$ 0.4