Stock-based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended				6 Months Ended		42 Months Ended
	Jul. 01, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2018
Stock-Based Compensation
Shares issued under the Employee Stock Purchase Plan		$ 211	$ 218	$ 148	$ 127
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)		3,517,347				3,517,347
Service-Based Stock Options
Stock-Based Compensation
Expiration period						10 years
Vesting period						4 years
Granted (in shares)		152,500				1,638,510
Grant date fair value (in dollars per share)		$ 11.94		$ 9.26		$ 12.74	$ 6.85
Restricted Stock or Unit Expense						$ 3,300
Service-Based Stock Options | Maximum
Stock-Based Compensation
Expiration period						10 years
Restricted Stock Units (RSUs)
Stock-Based Compensation
Granted (in shares)		10,500				186,922
Grant date fair value (in dollars per share)		$ 16.62				$ 17.71
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)								558,977
Subsequent Event | Employee Stock
Stock-Based Compensation
Shares issued under the Employee Stock Purchase Plan ( in shares )	18,729
Shares issued under the Employee Stock Purchase Plan	$ 300