Stockholders' Equity - Summary of Changes in Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended
	Apr. 01, 2018	Mar. 26, 2017	Dec. 31, 2017	Dec. 25, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders’ equity at beginning of period	$ 511.5	$ 276.4
Comprehensive loss:
Net loss	(2.2)	(10.0)
Change in cumulative translation adjustment	(0.1)	0.1
Comprehensive loss	(2.3)	(9.9)
Stock-based compensation	1.7	2.1
Issuance of common stock for cash	0.0	81.9
Issuance of common stock for employee stock purchase plan	1.8	1.4
Restricted stock units exchanged for taxes	0.0	(0.5)
Stockholders’ equity at end of period	$ 512.5	$ 351.4
ASC 606
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact from adoption of ASC 606 (Note 1)			$ (0.2)	$ 0.0