Condensed Consolidated Statement of Stockholders' Equity (Unaudited) (USD $) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Total
Beginning balance, shares (in thousands) at Dec. 30, 2017	54,697
Beginning balance, amount at Dec. 30, 2017	$ 55	$ 110,380	$ (56,601)	$ 53,834
Adjustment to retained earnings: cumulative effect of initially applying ASC 606			164	164
Exercise of stock options, shares (in thousands)	57
Exercise of stock options, amount		255		255
Repurchase of common stock, shares (in thousands)	(75)
Repurchase of common stock, amount		(404)		(404)
Vested restricted stock, shares (in thousands)	2
Vested restricted stock, amount				0
Share-based compensation, amount		1,258		1,258
Net loss			(8,443)	(8,443)
Ending balance, shares (in thousands) at Mar. 31, 2018	54,681
Ending balance, amount at Mar. 31, 2018	$ 55	111,489	(64,880)	46,664
Beginning balance, shares (in thousands) at Dec. 30, 2017	54,697
Beginning balance, amount at Dec. 30, 2017	$ 55	110,380	(56,601)	53,834
Adjustment to retained earnings: cumulative effect of initially applying ASC 606				164
Repurchase of common stock, amount				(404)
Share-based compensation, amount				3,069
Net loss				(16,493)
Ending balance, shares (in thousands) at Jun. 30, 2018	54,870
Ending balance, amount at Jun. 30, 2018	$ 55	113,375	(72,930)	40,500
Beginning balance, shares (in thousands) at Mar. 31, 2018	54,681
Beginning balance, amount at Mar. 31, 2018	$ 55	111,489	(64,880)	46,664
Exercise of stock options, shares (in thousands)	22
Exercise of stock options, amount		75		75
Share-based compensation, shares (in thousands)	167
Share-based compensation, amount		1,811		1,811
Net loss			(8,050)	(8,050)
Ending balance, shares (in thousands) at Jun. 30, 2018	54,870
Ending balance, amount at Jun. 30, 2018	$ 55	113,375	(72,930)	40,500
Beginning balance, shares (in thousands) at Dec. 31, 2018	55,089
Beginning balance, amount at Dec. 31, 2018	$ 55	116,876	(89,753)	27,178
Exercise of stock options, shares (in thousands)	65
Exercise of stock options, amount		107		107
Share-based compensation, shares (in thousands)	167
Share-based compensation, amount		2,029		2,029
Net loss			(8,337)	(8,337)
Ending balance, shares (in thousands) at Mar. 31, 2019	55,321
Ending balance, amount at Mar. 31, 2019	$ 55	119,012	(98,090)	20,977
Beginning balance, shares (in thousands) at Dec. 31, 2018	55,089
Beginning balance, amount at Dec. 31, 2018	$ 55	116,876	(89,753)	27,178
Adjustment to retained earnings: cumulative effect of initially applying ASC 606				$ 0
Exercise of stock options, shares (in thousands)				128
Repurchase of common stock, amount				$ 0
Share-based compensation, amount				3,788
Net loss				(16,092)
Ending balance, shares (in thousands) at Jun. 30, 2019	55,384
Ending balance, amount at Jun. 30, 2019	$ 55	120,935	(105,845)	15,145
Beginning balance, shares (in thousands) at Mar. 31, 2019	55,321
Beginning balance, amount at Mar. 31, 2019	$ 55	119,012	(98,090)	20,977
Exercise of stock options, shares (in thousands)	63
Exercise of stock options, amount		164		164
Share-based compensation, amount		1,759		1,759
Net loss			(7,755)	(7,755)
Ending balance, shares (in thousands) at Jun. 30, 2019	55,384
Ending balance, amount at Jun. 30, 2019	$ 55	$ 120,935	$ (105,845)	$ 15,145