Condensed Consolidated Statements of Income - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 28, 2017
Sep. 29, 2016
Sep. 28, 2017
Sep. 29, 2016
Dec. 29, 2016
Dec. 31, 2015
Dec. 25, 2014
Income Statement [Abstract]              
Net sales $ 343,923 $ 271,311 $ 995,266 $ 772,465 $ 1,050,759 $ 784,012 $ 584,588
Cost of sales 201,432 160,344 585,076 457,949 621,497 471,390 355,051
Gross profit 142,491 110,967 410,190 314,516 429,262 312,622 229,537
Operating expenses:              
Selling and store operating 85,023 68,219 251,424 197,055 271,876 202,637 146,485
General and administrative 22,172 16,633 59,571 46,813 64,025 49,917 38,984
Pre-opening 6,700 5,046 13,825 10,989 13,732 7,380 7,412
Litigation settlement 0 (3,500) 0 10,500 10,500 0 0
Total operating expenses 113,895 86,398 324,820 265,357 360,133 260,230 195,856
Operating income 28,596 24,569 85,370 49,159 69,129 52,392 33,681
Interest expense 2,610 2,401 11,377 7,362 12,803 9,386 8,949
Loss on extinguishment of debt 0 0 5,442 153 1,813 0 0
Income before income taxes 25,986 22,168 68,551 41,644 54,513 43,006 24,732
Provision for income taxes 2,731 7,949 13,739 15,312 11,474 16,199 9,634
Net income $ 23,255 $ 14,219 $ 54,812 $ 26,332 $ 43,039 $ 26,807 $ 15,098
Basic earnings per share $ 0.25 $ 0.17 $ 0.61 $ 0.32 $ 0.52 $ 0.32 $ 0.18
Diluted earnings per share $ 0.22 $ 0.16 $ 0.56 $ 0.30 $ 0.49 $ 0.31 $ 0.18