Basis of Presentation - Revenue Recognition (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017	Mar. 31, 2018	Dec. 31, 2017	Dec. 30, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
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
Basic	$ 0.45	$ 0.21	$ 0.60	$ 0.27
Diluted	$ 0.43	$ 0.20	$ 0.57	$ 0.26
Comprehensive income	$ 22,226	$ 10,255	$ 29,504	$ 13,254
Cash and cash equivalents	63,923	$ 50,282	63,923	$ 50,282		$ 34,029	$ 34,029	$ 39,210
Accounts receivable, net	74,970		74,970				60,308
Inventories	35,326		35,326				37,816
Contract assets, net	11,012		11,012
Prepaid expenses	2,757		2,757				2,490
Other current assets	7,899		7,899				9,873
Total current assets	195,887		195,887				144,516
Property, plant and equipment, net	93,433		93,433				84,133
Trade name and other intangible assets, net	111,725		111,725				115,043
Goodwill	108,060		108,060				108,060
Other assets, net	1,336		1,336				1,367
Total assets	510,441		510,441				453,119
Accounts payable and accrued liabilities	45,911		45,911				41,085
Current portion of long-term debt	303		303				294
Total current liabilities	46,214		46,214				41,379
Long-term debt, less current portion	215,081		215,081				212,679
Deferred income taxes	23,287		23,287				22,772
Other liabilities	17,015		17,015				964
Total liabilities	301,597		301,597				277,794
Total shareholders' equity	208,844		208,844				175,325
Total liabilities and shareholders' equity	510,441		510,441				$ 453,119
Adoption of Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales			8,700
Contract assets, net	11,012		11,012		$ 9,210	$ 8,176
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Adoption of Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales	(1,987)		(2,952)
Cost of sales	(1,459)		(1,886)
Gross profit	(528)		(1,066)
Selling, general and administrative expenses	100		185
Income from operations	(428)		(881)
Income before income taxes	(428)		(881)
Income tax expense	(108)		(225)
Net income	(320)		(656)
Comprehensive income	(320)		(656)
Inventories	7,528		7,528
Contract assets, net	(11,012)		(11,012)
Total current assets	(3,484)		(3,484)
Total assets	(3,484)		(3,484)
Accounts payable and accrued liabilities	(298)		(298)
Total current liabilities	(298)		(298)
Deferred income taxes	647		647
Total liabilities	(945)		(945)
Total shareholders' equity	(2,539)		(2,539)
Total liabilities and shareholders' equity	(3,484)		(3,484)
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Adoption of Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net sales	167,282		306,570
Cost of sales	107,863		202,916
Gross profit	59,419		103,654
Selling, general and administrative expenses	32,481		61,053
Gains on transfers of assets	(2,551)		(2,551)
Income from operations	29,489		45,152
Interest expense, net	3,609		7,652
Debt extinguishment costs			3,079
Income before income taxes	25,880		34,421
Income tax expense	3,652		5,189
Net income	$ 22,228		$ 29,232
Basic	$ 0.44		$ 0.58
Diluted	$ 0.43		$ 0.56
Comprehensive income	$ 21,906		$ 28,848
Cash and cash equivalents	63,923		63,923
Accounts receivable, net	74,970		74,970
Inventories	42,854		42,854
Prepaid expenses	2,757		2,757
Other current assets	7,899		7,899
Total current assets	192,403		192,403
Property, plant and equipment, net	93,433		93,433
Trade name and other intangible assets, net	111,725		111,725
Goodwill	108,060		108,060
Other assets, net	1,336		1,336
Total assets	506,957		506,957
Accounts payable and accrued liabilities	45,613		45,613
Current portion of long-term debt	303		303
Total current liabilities	45,916		45,916
Long-term debt, less current portion	215,081		215,081
Deferred income taxes	22,640		22,640
Other liabilities	17,015		17,015
Total liabilities	300,652		300,652
Total shareholders' equity	206,305		206,305
Total liabilities and shareholders' equity	$ 506,957		$ 506,957