Stockholders' Equity - Summary of Changes in Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 01, 2017	Sep. 25, 2016	Oct. 01, 2017	Sep. 25, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders’ equity at beginning of period			$ 276.4	$ 254.2
Comprehensive loss:
Net loss	$ (4.3)	$ (23.6)	(20.5)	(56.2)
Change in cumulative translation adjustment	(0.2)	(0.1)	(0.1)	(0.2)
Comprehensive loss	(4.5)	(23.7)	(20.6)	(56.4)
Exercise of stock options and warrants			0.4	0.0
Stock-based compensation			6.8	4.2
Issuance of common stock for cash			267.8	0.0
Issuance of common stock for employee stock purchase plan			3.1	2.6
Restricted stock units traded for taxes			(2.0)	(0.5)
Stockholders’ equity at end of period	$ 531.9	$ 204.1	$ 531.9	$ 204.1