Stockholders' Equity - Equity Offerings (Details) - Common Stock - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Jan. 01, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Oct. 07, 2020	Sep. 28, 2017
Equity offerings
Issuance of common stock, net of issuance costs, shares		3,092,603	5,161,502
2017 Sales Agreement
Equity offerings
Issuance of common stock, net of issuance costs, shares			4,136,742	0
Price per share			$ 3.52
Aggregate net proceeds from stock sale			$ 14.1
2017 Sales Agreement \| Maximum
Equity offerings
Common stock available for sale under agreement						$ 100.0
2020 Sales Agreement
Equity offerings
Issuance of common stock, net of issuance costs, shares		3,092,603	1,024,760
Price per share		$ 3.57	$ 3.74
Aggregate net proceeds from stock sale		$ 10.7	$ 3.7
Common stock available for sale under agreement		$ 85.1			$ 100.0
2020 Sales Agreement \| Subsequent Event
Equity offerings
Issuance of common stock, net of issuance costs, shares	0
2020 Sales Agreement \| Maximum
Equity offerings
Common stock available for sale under agreement					$ 100.0