Stock-based Compensation (Details) - USD ($)		3 Months Ended		12 Months Ended	39 Months Ended
	Apr. 03, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Mar. 31, 2018
Stock-Based Compensation
Stock-based compensation expense		$ 1,342,000	$ 502,000
Subsequent Event
Stock-Based Compensation
Employee Stock Purchase Plan, stock issued during period (in shares)	100,000
2004, 2001, 1992, and 2009 Plans
Stock-Based Compensation
Number of shares available for grant (in shares)		0			0
2017 Plan
Stock-Based Compensation
Number of shares available for grant (in shares)		3,081,651			3,081,651
Service-Based Stock Options
Stock-Based Compensation
Expiration period		10 years
Vesting period		4 years		4 years
Granted (in shares)		1,363,310
Grant date fair value (in dollars per share)		$ 6.63	$ 2.00
Stock-based compensation expense		$ 1,300,000	$ 500,000
Weighted average assumptions used to estimate fair value of each service-based stock option grant
Expected dividend rate		0.00%	0.00%
Service-Based Stock Options | Maximum
Stock-Based Compensation
Expiration period				10 years
Weighted average assumptions used to estimate fair value of each service-based stock option grant
Expected stock price volatility		84.40%	88.20%
Risk-free interest rate		2.80%	2.30%
Expected life		6 years 3 months 18 days	6 years 3 months 18 days
Service-Based Stock Options | Minimum
Weighted average assumptions used to estimate fair value of each service-based stock option grant
Expected stock price volatility		82.30%	81.30%
Risk-free interest rate		2.40%	2.00%
Expected life		6 years 1 month 4 days	6 years 1 month 4 days
Employee Stock
Stock-Based Compensation
Employee Stock Purchase Plan, number of shares authorized (in shares)		1,000,000			1,000,000
Employee Stock Purchase Plan, grants since inception (in shares)					461,434
Stock-based compensation expense			$ 100,000
Employee Stock | Subsequent Event
Stock-Based Compensation
Employee Stock Purchase Plan, stock issued during period (in shares)	$ 31,923