Consolidated Statements of Equity Statement (USD $) In Thousands, except Share data, unless otherwise specified		Total USD ($)	Common Stock [Member] USD ($)		Treasury Stock [Member] USD ($)	Additional Paid-in Capital [Member] USD ($)	Accumulated Other Comprehensive Loss [Member] USD ($)	Retained Earnings (Accumulated Deficit) [Member] USD ($)	Class B Common Stock [Member]	Class C Common Stock [Member]
Temporary equity, beginning balance at Jan. 03, 2012		$ 2,572
Beginning balance at Jan. 03, 2012		4,951	232	[1],[2]	0	6,291	(52)	(1,520)
Beginning balance, shares at Jan. 03, 2012			23,238,984	[2]	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options		27	0			27
Exercise of stock options, shares			0
Stock-based compensation expenses		(1,029)				1,315
2010 Merger-transaction expenses		1,315				(48)
Temporary equity related to put options		(48)
Treasury shares acquired								(1,029)
Unrealized income on cash flow hedges, net of tax		28					28
Net income		5,163						5,163
Increase (Decrease) in Temporary Equity [Roll Forward]
Temporary equity related to put options		1,029
Temporary equity, ending balance at Jan. 01, 2013		3,601
Ending balance at Jan. 01, 2013		10,407	232	[1],[2]	0	7,585	(24)	2,614
Ending balance, shares at Jan. 01, 2013	[2]		23,238,984		0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with IPO, net of transaction expenses		100,069	62	[2]		100,007
Issuance of common stock, net of transaction expenses, shares	[2]		6,160,714
Elimination of temporary equity at IPO		3,601				2,572		1,029
Proceeds from exercise of stock options, warrants and employee stock purchase plan		1,982	1	[2]		1,981
Proceeds from exercise of stock options, warrants and employee stock purchase plan, shares	[2]		144,907
Treasury shares acquired		(2,777)			(2,777)
Treasury shares acquired, shares					65,478
Stock-based compensation expenses		201				201
2010 Merger-transaction expenses		1,098				1,098
Stock-based compensation expense related to acceleration of vesting		3,203				3,203
Other		24					24
Other, shares	[2]		(48)
Net income		6,665						6,665
Increase (Decrease) in Temporary Equity [Roll Forward]
Elimination of temporary equity at IPO		(3,601)
Temporary equity related to put options		0
Temporary equity, ending balance at Dec. 31, 2013		0
Ending balance at Dec. 31, 2013		124,473	295	[1],[2]	(2,777)	116,647	0	10,308
Ending balance, shares at Dec. 31, 2013			29,544,557	[2]	65,478				6,292,640	1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from exercise of stock options, warrants and employee stock purchase plan		2,676	3	[2]		2,673
Proceeds from exercise of stock options, warrants and employee stock purchase plan, shares	[2]		275,783
Treasury shares acquired		(71)			(71)
Treasury shares acquired, shares					2,108
Stock-based compensation expenses		253				253
2010 Merger-transaction expenses		1,418				1,418
Other		(62)					0
Other, shares	[2]		0
Adjustments to Additional Paid in Capital, Other						(62)
Net income		11,428						11,428
Temporary equity, ending balance at Dec. 30, 2014		0
Ending balance at Dec. 30, 2014		$ 140,115	$ 298	[1],[2]	$ (2,848)	$ 120,929	$ 0	$ 21,736
Ending balance, shares at Dec. 30, 2014			29,820,340	[2]	67,586				1,522,098

[1] Includes 1,522,098 and 6,292,640 shares of Class B common stock as of December 30, 2014 and December 31, 2013, respectively, and one share of Class C common stock as of January 1, 2013

[2] Unless otherwise noted, activity relates to Class A common stock