Condensed Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Income Statement [Abstract]
Net sales	$ 169,269	$ 137,384	$ 309,522	$ 250,105
Cost of sales	109,322	92,831	204,802	173,813
Gross profit	59,947	44,553	104,720	76,292
Selling, general and administrative expenses	32,581	24,650	61,238	47,435
Gains on transfers of assets	(2,551)		(2,551)
Income from operations	29,917	19,903	46,033	28,857
Interest expense, net	3,609	4,568	7,652	9,478
Debt extinguishment costs			3,079
Income before income taxes	26,308	15,335	35,302	19,379
Income tax expense	3,760	5,080	5,414	6,125
Net income	$ 22,548	$ 10,255	$ 29,888	$ 13,254
Net income per common share:
Basic	$ 0.45	$ 0.21	$ 0.60	$ 0.27
Diluted	$ 0.43	$ 0.20	$ 0.57	$ 0.26
Weighted average shares outstanding:
Basic	50,317	49,473	50,087	49,368
Diluted	52,056	51,664	52,023	51,607
Comprehensive income	$ 22,226	$ 10,255	$ 29,504	$ 13,254