CONSOLIDATED BALANCE SHEETS (unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 30, 2017
Statement of Financial Position [Abstract]
Accumulated depreciation	$ 137,883	$ 131,260
Preferred stock, par value per share (in dollars per share)	$ 0.01000	$ 0.01000
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share (in dollars per share)	$ 0.01000	$ 0.01000
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	125,613,000	123,895,000
Common stock, shares outstanding	125,613,000	123,895,000