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Stock-based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended						9 Months Ended		42 Months Ended
	Oct. 01, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2018
Stock-Based Compensation
Shares issued under the Employee Stock Purchase Plan		$ 275	$ 211	$ 218	$ 200	$ 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)		3,605,081						3,605,081
Service-Based Stock Options
Stock-Based Compensation
Expiration period								10 years
Granted (in shares)		111,600						1,750,110
Vesting period								4 years
Grant date fair value (in dollars per share)		$ 13.28			$ 10.90			$ 12.77	$ 9.62
Restricted stock units, grant-date fair value								$ 3,300
Service-Based Stock Options \| Maximum
Stock-Based Compensation
Expiration period								10 years
Service-Based Stock Options \| Minimum
Stock-Based Compensation
Vesting period								4 years
Director options
Stock-Based Compensation
Vesting period								1 year
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)										576,723
Restricted Stock Units (RSUs)
Stock-Based Compensation
Granted (in shares)								186,922	0
Grant date fair value (in dollars per share)								$ 17.71
Subsequent Event \| Employee Stock
Stock-Based Compensation
Shares issued under the Employee Stock Purchase Plan ( in shares )	17,746
Shares issued under the Employee Stock Purchase Plan	$ 200