Dorman Products (DORM) 10-Q 30 Oct 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 29, 2018	Oct. 26, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 29, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	DORM
Entity Registrant Name	Dorman Products, Inc.
Entity Central Index Key	868,780
Current Fiscal Year End Date	--12-29
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		33,046,291

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net sales	$ 247,954	$ 224,615	$ 713,363	$ 675,502
Cost of goods sold	152,957	136,489	437,029	407,781
Gross profit	94,997	88,126	276,334	267,721
Selling, general and administrative expenses	51,264	45,336	149,828	134,890
Income from operations	43,733	42,790	126,506	132,831
Other income, net	61	168	286	472
Income before income taxes	43,794	42,958	126,792	133,303
Provision for income taxes	9,777	15,950	27,789	48,671
Net income	$ 34,017	$ 27,008	$ 99,003	$ 84,632
Earnings Per Share:
Basic	$ 1.03	$ 0.80	$ 2.98	$ 2.48
Diluted	$ 1.03	$ 0.80	$ 2.98	$ 2.47
Weighted Average Shares Outstanding:
Basic	32,985	33,822	33,177	34,111
Diluted	33,095	33,909	33,267	34,202

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 29, 2018	Dec. 30, 2017
Current assets:
Cash and cash equivalents	$ 53,113	$ 71,691
Accounts receivable, less allowance for doubtful accounts and customer credits of $99,847 and $97,193	301,049	241,880
Inventories	239,957	212,149
Prepaids and other current assets	7,838	7,129
Total current assets	601,957	532,849
Property, plant and equipment, net	96,794	92,692
Goodwill	80,065	65,999
Intangible assets, net	20,707	22,158
Deferred tax asset, net	4,297	7,884
Other assets	45,242	44,342
Total	849,062	765,924
Current liabilities:
Accounts payable	97,937	80,218
Accrued compensation	11,859	12,162
Other accrued liabilities	18,063	18,401
Total current liabilities	127,859	110,781
Other long-term liabilities	13,840	13,732
Deferred tax liabilities, net	5,410	6,604
Commitments and contingencies
Shareholders’ Equity:
Common stock, par value $0.01; authorized 50,000,000 shares; issued and outstanding 33,139,997 and 33,571,524 in 2018 and 2017, respectively	331	336
Additional paid-in capital	47,314	44,812
Retained earnings	654,308	589,659
Total shareholders’ equity	701,953	634,807
Total	$ 849,062	$ 765,924

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 29, 2018	Dec. 30, 2017
Statement Of Financial Position [Abstract]
Allowance for doubtful accounts and customer credits	$ 99,847	$ 97,193
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	33,139,997	33,571,524
Common stock, shares outstanding	33,139,997	33,571,524

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017
Cash Flows from Operating Activities:
Net income	$ 99,003	$ 84,632
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation, amortization and accretion	19,673	15,968
Provision for doubtful accounts	(586)	225
Provision (benefit) for deferred income taxes	3,584	(3,998)
Provision for non-cash stock compensation	3,129	2,282
Changes in assets and liabilities:
Accounts receivable	(56,484)	(793)
Inventories	(16,146)	(30,990)
Prepaids and other current assets	(2,071)	(1,232)
Other assets	(261)	(5,644)
Accounts payable	15,262	310
Accrued compensation and other liabilities	110	(1,398)
Cash provided by operating activities	65,213	59,362
Cash Flows from Investing Activities:
Acquisitions, net of cash acquired	(28,040)	(3,128)
Property, plant and equipment additions	(18,099)	(17,436)
Purchase of investments		(10,000)
Cash used in investing activities	(46,139)	(30,564)
Cash Flows from Financing Activities:
Contingent consideration	(2,036)
Other stock related activity	(364)	(997)
Purchase and cancellation of common stock	(35,224)	(60,133)
Cash used in financing activities	(37,624)	(61,130)
Effect of exchange rate changes on Cash and Cash Equivalents	(28)
Net Decrease in Cash and Cash Equivalents	(18,578)	(32,332)
Cash and Cash Equivalents, Beginning of Period	71,691	149,121
Cash and Cash Equivalents, End of Period	53,113	116,789
Supplemental Cash Flow Information
Cash paid for interest expense	191	218
Cash paid for income taxes	$ 21,722	$ 55,713

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 29, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	1. Basis of Presentation As used herein, unless the context otherwise requires, “Dorman”, the “Company”, “we”, “us”, or “our” refers to Dorman Products, Inc. and its subsidiaries. Our ticker symbol on the NASDAQ Global Select Market is “DORM”. The accompanying unaudited consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the U.S. for interim financial information and in accordance with the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”). However, they do not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments (consisting of only normal recurring adjustments) considered necessary for a fair presentation have been included. Operating results for the thirty-nine weeks ended September 29, 2018 are not necessarily indicative of the results that may be expected for the fiscal year ending December 29, 2018. We may experience significant fluctuations from quarter to quarter in our results of operations due to the timing of orders placed by our customers. The introduction of new products and product lines to customers may cause significant fluctuations from quarter to quarter. These financial statements should be read in conjunction with the consolidated financial statements and footnotes thereto included in our Annual Report on Form 10-K for the fiscal year ended December 30, 2017.

Business Acquisitions and Inves

Business Acquisitions and Investments	9 Months Ended
	Sep. 29, 2018
Business Combinations [Abstract]
Business Acquisitions and Investments	2. Business Acquisitions and Investments On August 31, 2018, we acquired 100% of the outstanding stock of Flight Systems Automotive Group LLC (“Flight Systems” or “Flight”), a privately-held manufacturer and remanufacturer of complex automotive electronics and diesel fuel system components, based in Lewisberry, Pennsylvania. We paid $27.5 million in cash which is subject to customary purchase price adjustments. In connection with this acquisition, we preliminary recorded $13.3 million in goodwill and $14.2 million of other net assets, primarily $2.0 million of accounts receivables, $11.6 million of inventory, and $0.6 million of net other assets and liabilities. We expect that, upon completion of our valuation, we will recognize intangible assets with an offsetting reduction in the preliminary goodwill that was recognized as of September 29, 2018. The purchase price allocation is preliminary and subject to adjustment as we complete our assessment of the fair values of acquired assets and assumed liabilities. We believe that the goodwill and intangible assets resulting from the acquisition will be deductible for tax purposes. The financial results of the acquisition have been included in the Consolidated Financial Statements since the date of acquisition. Flight generated $1.7 million of net sales and an immaterial amount of net income since the date of acquisition. We believe complex electronics and diesel fuel system components represent important growth opportunities for us and Flight’s product portfolio delivers valuable alternatives to aftermarket professionals. On October 26, 2017, we acquired 100% of the outstanding stock of MAS Automotive Distribution Inc. (“MAS Industries” or “MAS”), a privately-held manufacturer of premium chassis and control arms based in Montreal, Canada. The purchase price was $67.2 million net of $3.3 million of cash acquired and including contingent consideration at fair value and other purchase price adjustments. We believe MAS is complementary to our business and growth strategy. We see opportunities to leverage MAS’ existing presence in the automotive aftermarket, as well as our product development capabilities and financial resources to accelerate the growth of MAS’ premium chassis and control arm products. We have included the results of MAS in our Consolidated Financial Statements since the acquisition date of October 26, 2017. The Consolidated Statement of Operations for the thirty-nine weeks ended September 29, 2018 includes $30.0 million of net sales and an immaterial amount of net income related to MAS. The Consolidated Balance Sheets as of September 29, 2018 and December 30, 2017 reflects the acquisition of MAS Industries, effective October 26, 2017. The following table summarizes the fair value of the total consideration related to MAS: (in thousands) Total Acquisition Date Fair Value Cash consideration (net of $3.3 million cash acquired) $ 56,859 Contingent cash consideration 7,982 Seller liability assumed 896 Working capital adjustment 1,486 Total consideration assigned to net assets acquired $ 67,223 Included in the table above is $8.0 million of estimated contingent payments which represents the fair value of the estimated payments which will become due if certain sales thresholds are achieved through December 2020. The fair value of the contingent cash consideration was estimated by using an option pricing model framework, which represents our own assumptions and data, and is based on our best available information. As of September 29, 2018, we had $8.2 million recorded which includes $0.2 million of accretion which was included in Selling, General and Administrative expenses for the thirty-nine weeks ended September 29, 2018, related to this payment. The maximum contingent payment would be $11.7 million. Additionally, during the thirty-nine weeks ended September 29, 2018, we finalized working capital and other purchase price adjustments based on the MAS standalone audited 2017 financial statements, resulting in a payment to the former shareholder of $1.5 million. This amount had previously been accrued on our Consolidated Balance Sheet. The transaction was accounted for as a business combination under the acquisition method of accounting. Accordingly, the assets acquired and liabilities assumed were recorded at fair value, with the remaining purchase price recorded as goodwill. The following table summarizes the fair values of the assets acquired and liabilities assumed as of October 26, 2017: (in thousands) October 26, 2017 (As initially reported) Measurement period adjustments October 26, 2017 (As adjusted) Current assets (net of $3.3 million cash acquired) $ 21,756 $ 90 $ 21,846 Property, plant and equipment 1,615 - 1,615 Intangible assets 20,440 - 20,440 Goodwill 35,624 (193 ) 35,431 Total assets acquired 79,435 (103 ) 79,332 Current liabilities 5,691 (50 ) 5,641 Long-term liabilities 6,468 - 6,468 Total liabilities assumed 12,159 (50 ) 12,109 Net assets acquired $ 67,276 $ (53 ) $ 67,223 Our measurement period adjustments for MAS were complete as of September 29, 2018. The valuation of the intangible assets acquired and related amortization periods are as follows: (in thousands) Valuation Amortization Period (in years) Customer relationships $ 14,840 8-12 Tradenames 5,600 15 Total $ 20,440 The fair values of the Customer Relationships and Tradenames were estimated using a discounted present value income approach. Under this method, an intangible asset’s fair value is equal to the present value of the incremental after-tax cash flows (excess earnings) attributable solely to the intangible asset over its remaining useful life. To calculate fair value, we used cash flows discounted at rates ranging from 15% to 17%, which were considered appropriate given the inherent risk associated with each type of asset. We believe that the level and timing of cash flows appropriately reflect market participant assumptions. The goodwill recognized is attributable primarily to strategic and synergistic opportunities related to existing automotive aftermarket businesses, the assembled workforce of MAS and other factors. The goodwill is expected to be deductible for tax purposes. Pro Forma Financial Information (Unaudited) The unaudited pro forma information for the periods set forth below give effect to the MAS acquisition as if it occurred as of December 27, 2015, the start of our 2016 fiscal year. The pro forma information is presented for informational purposes only and is not necessarily indicative of the results of the operations that actually would have been achieved had the acquisition been consummated as of that time: Thirty-Nine Weeks Ended (in thousands) September 30, 2017 Net sales $ 702,811 Net income $ 85,307 Diluted earnings per share $ 2.49 The unaudited pro forma net income for the thirty-nine weeks ended September 30, 2017 was adjusted to include amortization of intangible assets, accretion for contingent consideration liabilities and to exclude financing costs of MAS which we do not believe would have occurred.

Sales of Accounts Receivable

Sales of Accounts Receivable	9 Months Ended
	Sep. 29, 2018
Receivables [Abstract]
Sales of Accounts Receivable	3. Sales of Accounts Receivable We have entered into several customer sponsored programs administered by unrelated financial institutions that permit us to sell certain accounts receivable at discounted rates to the financial institutions. Transactions under these agreements were accounted for as sales of accounts receivable and were removed from our Consolidated Balance Sheet at the time of the sales transactions. Pursuant to these agreements, we sold $438.6

Inventories

Inventories	9 Months Ended
	Sep. 29, 2018
Inventory Disclosure [Abstract]
Inventories	4. Inventories Inventories include the cost of material, freight, direct labor and overhead utilized in the processing of our products, and are stated at the lower of cost or net realizable value. Inventories were as follows: (in thousands) September 29, 2018 December 30, 2017 Bulk product $ 93,142 $ 82,010 Finished product 143,118 126,827 Packaging materials 3,697 3,312 Total $ 239,957 $ 212,149

Goodwill and Intangible Assets

Goodwill and Intangible Assets	9 Months Ended
	Sep. 29, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	5. Goodwill and Intangible Assets Goodwill Goodwill included the following: (in thousands) September 29, 2018 December 30, 2017 Balance at beginning of period $ 65,999 $ 28,146 Goodwill acquired 14,368 37,853 Measurement period adjustments (302 ) - Balance at end of period $ 80,065 $ 65,999 Intangible Assets Intangible assets included the following: September 29, 2018 December 30, 2017 (in thousands) Weighted Average Amortization Period Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Intangible assets subject to amortization Tradenames 14.1 $ 5,600 $ 373 $ 5,227 $ 5,600 $ 62 $ 5,538 Customer relationships 9.5 17,049 1,893 15,156 17,049 772 16,277 Technology 13.3 367 43 324 367 24 343 Total $ 23,016 $ 2,309 $ 20,707 $ 23,016 $ 858 $ 22,158 Amortization expense was $1.6 million and less than $0.1 million for the thirty-nine weeks ended September 29, 2018 and September 30, 2017, respectively .

Revenue Recognition

Revenue Recognition	9 Months Ended
	Sep. 29, 2018
Revenue From Contract With Customer [Abstract]
Revenue Recognition	6. Revenue Recognition The FASB issued an accounting standard update in May 2014 regarding the accounting for and disclosure of revenue. Specifically, the update outlined a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers, which is common to both U.S. GAAP and International Financial Reporting Standards. Our primary source of revenue is from contracts with and purchase orders from customers. Revenue is recognized from product sales when goods are shipped, title and risk of loss and control have been transferred to the customer, and collection is reasonably assured. We estimate the transaction price at the inception of a contract or upon fulfilling a purchase order, including any variable consideration, and will update the estimate for changes in circumstances. We utilize the most likely amount method consistently to estimate the effect of uncertainty on the amount of variable consideration to which we would be entitled. The most likely amount method considers the single most likely amount from a range of possible consideration amounts. This method is utilized for all of our variable consideration. We record estimates for cash discounts, product returns, promotional rebates, core return deposits and other discounts in the period the related product revenue is recognized (“Customer Credits”). The provision for Customer Credits is recorded as a reduction from gross sales and reserves for Customer Credits are shown as a reduction of accounts receivable. Accrued customer rebates which we expect to settle in cash are classified as other accrued liabilities. Actual Customer Credits have not differed materially from estimated amounts for each period presented. Amounts billed to customers for shipping and handling are included in net sales. Costs associated with shipping and handling are included in cost of goods sold. We have concluded that our estimates of variable consideration are not constrained according to the definition of the new standard. All of our revenue was recognized under the point of time approach in accordance with the revenue standard during the thirty-nine weeks ended September 29, 2018 and September 30, 2017, respectively. Also, we do not have significant financing arrangements with our customers, as our credit terms are all less than one year. Lastly, we do not receive noncash consideration (such as materials or equipment) from our customers to facilitate the fulfillment of our contracts. Five-step model We apply the FASB’s guidance on revenue recognition, which requires us to recognize the amount of revenue and consideration which we expect to receive in exchange for goods or services transferred to our customers. To do this, we apply the five-step model prescribed by the FASB, which requires us to: (i) identify the contract with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when, or as, we satisfy a performance obligation. Contract Assets and Liabilities We recognize a receivable or contract asset when we perform a service or transfer a good in advance of receiving consideration. - A receivable is recorded when our right to consideration is unconditional and only the passage of time is required before payment of that consideration is due. - A contract asset is recorded when our right to consideration in exchange for goods or services that we have transferred to a customer is conditional on something other than the passage of time. We did not have any contract assets recorded as of September 29, 2018 or December 30, 2017. We recognize a contract liability when we receive consideration, or if we have the unconditional right to receive consideration, in advance of satisfying the performance obligation. A contract liability is our obligation to transfer goods or services to a customer for which we have received consideration, or an amount of consideration is due from the customer. We did not have any contract liabilities recorded as of September 29, 2018 or December 30, 2017. Disaggregated Revenue The following tables present our disaggregated net sales by Type of Major Good / Product Line, and Geography. Thirteen Weeks Ended Thirty-Nine Weeks Ended (in thousands) September 29, 2018 September 30, 2017 September 29, 2018 September 30, 2017 Powertrain $ 100,994 $ 94,177 $ 295,363 $ 284,393 Chassis 69,214 57,281 206,483 173,498 Automotive Body 67,000 62,791 179,539 185,804 Hardware 10,746 10,366 31,978 31,807 Net Sales $ 247,954 $ 224,615 $ 713,363 $ 675,502 Thirteen Weeks Ended Thirty-Nine Weeks Ended (in thousands) September 29, 2018 September 30, 2017 September 29, 2018 September 30, 2017 Net Sales to U.S. Customers $ 229,761 $ 210,347 $ 663,212 $ 634,422 Net Sales to Non-U.S. Customers 18,193 14,268 50,151 41,080 Net Sales $ 247,954 $ 224,615 $ 713,363 $ 675,502

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 29, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	7. Stock-Based Compensation On May 16, 2018, our shareholders approved our 2018 Stock Option and Stock Incentive Plan (the “2018 Plan” or the “Plan”), which supersedes our 2008 Stock Option and Stock Incentive Plan. All future stock compensation grants will be issued under the 2018 Plan. Under the terms of the Plan, our Board of Directors may grant up to 1,200,000 shares of common stock in the form of shares of restricted stock, restricted stock units, stock appreciation rights and stock options or combinations thereof to officers, directors, employees, important consultants and advisors. Grants under the Plan must be made within ten years of the date the Plan was approved. Stock options are exercisable upon the terms set forth in each grant agreement approved by the Board of Directors, but in no event more than ten years from the date of grant. Restricted stock and restricted stock units vest in accordance with the terms set forth in each applicable award agreement approved by our Board of Directors. At September 29, 2018, 1,184,305 shares were available for grant under the 2018 Plan. Restricted Stock We grant restricted stock to certain employees and members of our Board of Directors. The value of restricted stock issued is based on the fair value of our common stock on the grant date. Vesting of restricted stock is conditional based on continued employment or service for a specified period and, in certain circumstances, the attainment of financial goals. We retain the restricted stock, and any dividends paid thereon, until the vesting conditions have been met. For awards with a service condition only, compensation cost related to the stock is recognized on a straight-line basis over the vesting period. For awards that have a service condition and require the attainment of financial goals, compensation cost related to the stock is calculated based upon the probable outcome of the performance conditions on the date of grant and is recognized over the performance period. Compensation cost related to restricted stock was $2.5 million and $2.1 million for the thirty-nine weeks ended September 29, 2018 and September 30, 2017, respectively. The following table summarizes our restricted stock activity for the thirty-nine weeks ended September 29, 2018: Shares Weighted Average Price Balance at December 30, 2017 153,727 $ 59.96 Granted 80,872 $ 72.19 Vested (38,631 ) $ 61.07 Cancelled (6,237 ) $ 75.59 Balance at September 29, 2018 189,731 $ 64.43 As of September 29, 2018, there was $5.2 million of unrecognized compensation cost related to nonvested restricted stock, which is expected to be recognized over a weighted-average period of approximately 2.3 years. Cash flows resulting from tax deductions in excess of the tax effect of compensation cost recognized in the financial statements are classified as operating cash flows. The excess tax benefit generated from restricted shares which vested in the thirty-nine weeks ended September 29, 2018 was less than $0.1 million and was credited to income tax expense. The excess tax benefit generated from restricted shares which vested in the thirty-nine weeks ended September 30, 2017 was $0.3 million and was credited to income tax expense. Stock Options We grant stock options to certain employees. We expense the grant-date fair value of stock options. Compensation cost is recognized on a straight-line basis over the vesting period for which related services are performed. The compensation cost charged against income was $0.4 million and $0.2 million for the thirty-nine weeks ended September 29, 2018 and September 30, 2017, respectively. The compensation costs were classified as Selling, general and administrative expense in the Consolidated Statements of Income. No cost was capitalized during the thirty-nine weeks ended September 29, 2018 and September 30, 2017. We use the Black-Scholes option valuation model to estimate the fair value of stock options granted. Expected volatility and expected dividend yield are based on the actual historical experience of our common stock. The expected life represents the period of time that options granted are expected to be outstanding and was calculated using historical option exercise data. The risk-free rate was based on a U.S. Treasury security with terms equal to the expected time of exercise as of the grant date. During the thirty-nine weeks ended September 29, 2018 and September 30, 2017 we granted 69,014 and 58,024 stock options, respectively. The following table summarizes our stock option activity for the thirty-nine weeks ended September 29, 2018: Shares Weighted Average Exercise Price Weighted Average Remaining Term (In years) Aggregate Intrinsic Value Balance at December 30, 2017 122,547 $ 57.74 Granted 69,014 $ 72.32 Exercised (4,000 ) $ 5.67 Balance at September 29, 2018 187,561 $ 64.21 3.7 $ 2,490,355 Options exercisable at September 29, 2018 47,079 $ 51.55 2.6 $ 1,220,858 There were 4,000 options exercised during the thirty-nine weeks ended September 29, 2018. There were 32,000 options exercised in the thirty-nine weeks ended September 30, 2017. As of September 29, 2018, there was $1.6 million of unrecognized compensation cost related to non-vested stock options, which is expected to be recognized over a weighted-average period of 2.9 years. There was no cash generated from stock option exercises in the thirty-nine weeks ended September 29, 2018. The cash received from stock option exercises was $0.1 million in the thirty-nine weeks ended September 30, 2017. T here was no excess tax benefit generated from stock options exercised in the thirty-nine weeks ended September 29, 2018. There was $0.6 million of excess tax benefit generated from stock option exercises in the thirty-nine weeks ended September 30, 2017 and was credited to income tax expense. Employee Stock Purchase Plan In May 2017, our shareholders’ approved the Dorman Products, Inc. Employee Stock Purchase Plan (the “ESPP”), which makes available 1,000,000 shares of our common stock for sale to eligible employees. There were 7,382 shares purchased under this plan in the thirty-nine weeks ended September 29, 2018. During the thirty-nine weeks ended September 29, 2018, compensation cost under the Plan was $0.2 million.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 29, 2018
Earnings Per Share [Abstract]
Earnings Per Share	8. Earnings Per Share Basic earnings per share is calculated by dividing our net income by the weighted average number of common shares outstanding during the period, excluding nonvested restricted stock which is considered to be contingently issuable. To calculate diluted earnings per share, common share equivalents are added to the weighted average number of common shares outstanding. Common share equivalents are calculated using the treasury stock method and are computed based on outstanding stock-based awards. Stock-based awards of 63,000 shares and 47,500 shares were excluded from the calculation of diluted earnings per share as of September 29, 2018 and September 30, 2017, respectively, as their effect would have been anti-dilutive. The following table sets forth the computation of basic earnings per share and diluted earnings per share: Thirteen Weeks Ended Thirty-Nine Weeks Ended (in thousands, except per share data) September 29, 2018 September 30, 2017 September 29, 2018 September 30, 2017 Numerator Net income $ 34,017 $ 27,008 $ 99,003 $ 84,632 Denominator: Weighted average basic shares outstanding 32,985 33,822 33,177 34,111 Effect of stock-based compensation awards 110 87 90 91 Weighted average diluted shares outstanding 33,095 33,909 33,267 34,202 Earnings Per Share: Basic $ 1.03 $ 0.80 $ 2.98 $ 2.48 Diluted $ 1.03 $ 0.80 $ 2.98 $ 2.47

Common Stock Repurchases

Common Stock Repurchases	9 Months Ended
	Sep. 29, 2018
Text Block [Abstract]
Common Stock Repurchases	9. Common Stock Repurchases We periodically repurchase, at the then current market price, and cancel common stock issued to the Dorman Products, Inc. 401(k) Retirement Plan and Trust (the “401(k) Plan”). Shares are generally purchased from the 401(k) Plan when participants sell units as permitted by the 401(k) Plan or elect to leave the 401(k) Plan upon retirement, termination or other reasons. For the thirty-nine weeks ended September 29, 2018, we repurchased and cancelled 20,160 shares of common stock for $1.5 million at an average price of $73.35 per share. During the fifty-two weeks ended December 30, 2017, we repurchased and cancelled 19,110 shares of common stock for $1.4 million at an average price of $73.34 per share. Our Board of Directors authorized a share repurchase program of up to $250 million through December 31, 2018. Under this program, share repurchases may be made from time to time depending on market conditions, share price, share availability and other factors at our discretion. The share repurchase program does not obligate us to acquire any specific number of shares. For the thirty-nine weeks ended September 29, 2018, we repurchased and cancelled 486,487 shares of common stock for $33.8 million at an average price of $69.41 per share under this program. For the fifty-two weeks ended December 30, 2017, we repurchased and cancelled 1,006,365 shares of common stock for $74.7 million at an average price of $74.26 per share under this program.

Related-Party Transactions

Related-Party Transactions	9 Months Ended
	Sep. 29, 2018
Related Party Transactions [Abstract]
Related-Party Transactions	10. Related-Party Transactions We have a non-cancelable operating lease for our primary operating facility with a partnership in which Steven L. Berman, our Executive Chairman, and his family members, are partners. Based upon the terms of the lease, payments will be $1.6 million in fiscal 2018 and were $1.6 million in fiscal 2017. This lease will expire on December 31, 2022. In the opinion of our Audit Committee, the terms and rates of this lease are no less favorable than those which could have been obtained from an unaffiliated party when the lease was renewed during November 2016. Additionally, we have a non-cancelable operating lease for our Canadian operating facility from a corporation of which an employee, who is also the former owner of MAS, and his family members are owners. Based upon the terms of the lease, payments will be $0.5 million in fiscal 2018 and were $0.1 million in fiscal 2017. This lease will expire on January 31, 2019. We are a partner in a joint venture with one of our suppliers and own minority interests in two other suppliers. Each of these investments is accounted for according to the equity method. In June 2018 we acquired the remaining outstanding shares of a previously unconsolidated entity. The estimated fair value of the net assets acquired was less than our prior investment in the entity. As a result, we recorded an impairment charge of $1.1 million which is included within Selling, General, and Administrative expenses in the Consolidated Statement of Income during the thirty-nine weeks ended September 29, 2018.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 29, 2018
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes At September 29, 2018, we had $2.5 million of net unrecognized tax benefits, $2.2 million of which would affect our effective tax rate if recognized. We recognize interest and penalties related to uncertain tax positions in income tax expense. As of September 29, 2018 we had approximately $0.7 million of accrued interest and penalties related to uncertain tax positions. We file income tax returns in the United States, Canada, India, and Mexico. All years before 2015 are closed for federal tax purposes. Tax years before 2013 are closed for the all states in which we file. We filed tax returns in Sweden through 2012 and all years prior to 2010 are closed. It is reasonably possible that audit settlements, the conclusion of current examinations or the expirations of the statute of limitations could impact the Company’s unrecognized tax benefits. On December 22, 2017, the Tax Cuts and Jobs Act (the “TCJA”) was enacted. The TCJA includes a number of changes to existing U.S. tax laws that impact the Company, most notably a reduction of the U.S. corporate tax rate from 35% to 21%, for tax years beginning after December 31, 2017. The TCJA also provides for acceleration of depreciation for certain assets placed into service after September 27, 2017, as well as prospective changes beginning in 2018, including additional limitations on deductibility of executive compensation and employee meal benefits. As permitted by SEC Staff Accounting Bulletin (“SAB No. 118”), the net tax expense recorded in our financial statements for the fourth fiscal quarter of 2017 due to the enactment of the TCJA is considered “provisional” based on reasonable estimates. The net tax expense recorded was $4.4 million. We are continuing to collect and analyze detailed information that could impact this amount, and may record adjustments to refine those estimates during the measurement period defined in SAB No. 118, as additional analysis is completed. No adjustments to the provisional expense related to the enactment of the TCJA were recorded in the thirty-nine weeks ended September 29, 2018.

Fair Value Disclosures

Fair Value Disclosures	9 Months Ended
	Sep. 29, 2018
Fair Value Disclosures [Abstract]
Fair Value Disclosures	12. Fair Value Disclosures The carrying value of financial instruments such as cash, accounts receivable, accounts payable, and other current assets and liabilities approximate their fair value based on the short-term nature of these instruments.

New and Recently Adopted Accoun

New and Recently Adopted Accounting Pronouncements	9 Months Ended
	Sep. 29, 2018
Accounting Changes And Error Corrections [Abstract]
New and Recently Adopted Accounting Pronouncements	13. New and Recently Adopted Accounting Pronouncements On December 31, 2017, the beginning of our 2018 fiscal year, we adopted ASU No. 2014-09, Revenue from Contracts with Customers In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments – Overall In February 2016, the FASB issued ASU No. 2016-02, Leases in August 2018, the FASB issued ASU 2018-11, Targeted Improvements to ASC 842 , which includes an option to not restate comparative periods in transition and elect to use the effective date of ASC 842 as the date of initial application of transition. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment In June 2018, the FASB issued ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting

New and Recently Adopted Acco_2

New and Recently Adopted Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 29, 2018
Accounting Changes And Error Corrections [Abstract]
New and Recently Adopted Accounting Pronouncements	On December 31, 2017, the beginning of our 2018 fiscal year, we adopted ASU No. 2014-09, Revenue from Contracts with Customers In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments – Overall In February 2016, the FASB issued ASU No. 2016-02, Leases in August 2018, the FASB issued ASU 2018-11, Targeted Improvements to ASC 842 , which includes an option to not restate comparative periods in transition and elect to use the effective date of ASC 842 as the date of initial application of transition. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment In June 2018, the FASB issued ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting

Business Acquisitions and Inv_2

Business Acquisitions and Investments (Tables)	9 Months Ended
	Sep. 29, 2018
Business Combinations [Abstract]
Summary of Preliminary Fair Value of Total Consideration	The following table summarizes the fair value of the total consideration related to MAS: (in thousands) Total Acquisition Date Fair Value Cash consideration (net of $3.3 million cash acquired) $ 56,859 Contingent cash consideration 7,982 Seller liability assumed 896 Working capital adjustment 1,486 Total consideration assigned to net assets acquired $ 67,223
Summary of Preliminary Fair Values of Assets Acquired and Liabilities Assumed	The following table summarizes the fair values of the assets acquired and liabilities assumed as of October 26, 2017: (in thousands) October 26, 2017 (As initially reported) Measurement period adjustments October 26, 2017 (As adjusted) Current assets (net of $3.3 million cash acquired) $ 21,756 $ 90 $ 21,846 Property, plant and equipment 1,615 - 1,615 Intangible assets 20,440 - 20,440 Goodwill 35,624 (193 ) 35,431 Total assets acquired 79,435 (103 ) 79,332 Current liabilities 5,691 (50 ) 5,641 Long-term liabilities 6,468 - 6,468 Total liabilities assumed 12,159 (50 ) 12,109 Net assets acquired $ 67,276 $ (53 ) $ 67,223
Schedule of Valuation of Intangible Assets Acquired and Related Amortization Periods	The valuation of the intangible assets acquired and related amortization periods are as follows: (in thousands) Valuation Amortization Period (in years) Customer relationships $ 14,840 8-12 Tradenames 5,600 15 Total $ 20,440
Schedule of Pro Forma Financial Information	The pro forma information is presented for informational purposes only and is not necessarily indicative of the results of the operations that actually would have been achieved had the acquisition been consummated as of that time: Thirty-Nine Weeks Ended (in thousands) September 30, 2017 Net sales $ 702,811 Net income $ 85,307 Diluted earnings per share $ 2.49

Inventories (Tables)

Inventories (Tables)	9 Months Ended
	Sep. 29, 2018
Inventory Disclosure [Abstract]
Inventories	Inventories include the cost of material, freight, direct labor and overhead utilized in the processing of our products, and are stated at the lower of cost or net realizable value. Inventories were as follows: (in thousands) September 29, 2018 December 30, 2017 Bulk product $ 93,142 $ 82,010 Finished product 143,118 126,827 Packaging materials 3,697 3,312 Total $ 239,957 $ 212,149

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	9 Months Ended
	Sep. 29, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Goodwill Goodwill included the following: (in thousands) September 29, 2018 December 30, 2017 Balance at beginning of period $ 65,999 $ 28,146 Goodwill acquired 14,368 37,853 Measurement period adjustments (302 ) - Balance at end of period $ 80,065 $ 65,999
Schedule of Intangible Assets	Intangible Assets Intangible assets included the following: September 29, 2018 December 30, 2017 (in thousands) Weighted Average Amortization Period Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Intangible assets subject to amortization Tradenames 14.1 $ 5,600 $ 373 $ 5,227 $ 5,600 $ 62 $ 5,538 Customer relationships 9.5 17,049 1,893 15,156 17,049 772 16,277 Technology 13.3 367 43 324 367 24 343 Total $ 23,016 $ 2,309 $ 20,707 $ 23,016 $ 858 $ 22,158

Revenue Recognition (Tables)

Revenue Recognition (Tables)	9 Months Ended
	Sep. 29, 2018
Revenue From Contract With Customer [Abstract]
Summary of Disaggregated Net Sales	The following tables present our disaggregated net sales by Type of Major Good / Product Line, and Geography. Thirteen Weeks Ended Thirty-Nine Weeks Ended (in thousands) September 29, 2018 September 30, 2017 September 29, 2018 September 30, 2017 Powertrain $ 100,994 $ 94,177 $ 295,363 $ 284,393 Chassis 69,214 57,281 206,483 173,498 Automotive Body 67,000 62,791 179,539 185,804 Hardware 10,746 10,366 31,978 31,807 Net Sales $ 247,954 $ 224,615 $ 713,363 $ 675,502 Thirteen Weeks Ended Thirty-Nine Weeks Ended (in thousands) September 29, 2018 September 30, 2017 September 29, 2018 September 30, 2017 Net Sales to U.S. Customers $ 229,761 $ 210,347 $ 663,212 $ 634,422 Net Sales to Non-U.S. Customers 18,193 14,268 50,151 41,080 Net Sales $ 247,954 $ 224,615 $ 713,363 $ 675,502

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 29, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Restricted Stock Activity	The following table summarizes our restricted stock activity for the thirty-nine weeks ended September 29, 2018: Shares Weighted Average Price Balance at December 30, 2017 153,727 $ 59.96 Granted 80,872 $ 72.19 Vested (38,631 ) $ 61.07 Cancelled (6,237 ) $ 75.59 Balance at September 29, 2018 189,731 $ 64.43
Summary of Stock Option Activity	The following table summarizes our stock option activity for the thirty-nine weeks ended September 29, 2018: Shares Weighted Average Exercise Price Weighted Average Remaining Term (In years) Aggregate Intrinsic Value Balance at December 30, 2017 122,547 $ 57.74 Granted 69,014 $ 72.32 Exercised (4,000 ) $ 5.67 Balance at September 29, 2018 187,561 $ 64.21 3.7 $ 2,490,355 Options exercisable at September 29, 2018 47,079 $ 51.55 2.6 $ 1,220,858

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 29, 2018
Earnings Per Share [Abstract]
Schedule of Computation of Basic Earnings per Share and Diluted Earnings per Share	The following table sets forth the computation of basic earnings per share and diluted earnings per share: Thirteen Weeks Ended Thirty-Nine Weeks Ended (in thousands, except per share data) September 29, 2018 September 30, 2017 September 29, 2018 September 30, 2017 Numerator Net income $ 34,017 $ 27,008 $ 99,003 $ 84,632 Denominator: Weighted average basic shares outstanding 32,985 33,822 33,177 34,111 Effect of stock-based compensation awards 110 87 90 91 Weighted average diluted shares outstanding 33,095 33,909 33,267 34,202 Earnings Per Share: Basic $ 1.03 $ 0.80 $ 2.98 $ 2.48 Diluted $ 1.03 $ 0.80 $ 2.98 $ 2.47

Business Acquisitions and Inv_3

Business Acquisitions and Investments - Additional Information (Detail) - USD ($)	Aug. 31, 2018	Oct. 26, 2017	Sep. 29, 2018	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017	Dec. 30, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Business acquisition, goodwill			$ 80,065,000	$ 80,065,000		$ 80,065,000		$ 65,999,000	$ 28,146,000
Net sales				$ 247,954,000	$ 224,615,000	713,363,000	$ 675,502,000
Minimum [Member]
Business Acquisition [Line Items]
Cash flows discounted at rates		15.00%
Maximum [Member]
Business Acquisition [Line Items]
Cash flows discounted at rates		17.00%
Flight Systems Automotive Group LLC [Member]
Business Acquisition [Line Items]
Business acquisition, percentage of outstanding stock acquired	100.00%
Business acquisition, cash paid	$ 27,500,000
Business acquisition, goodwill	13,300,000
Business acquisition, other net assets	14,200,000
Business acquisition, accounts receivables	2,000,000
Business acquisition, inventory	11,600,000
Business acquisition, other assets and liabilities net	$ 600,000
Net sales			$ 1,700,000
MAS Automotive Distribution Inc [Member]
Business Acquisition [Line Items]
Business acquisition, percentage of outstanding stock acquired		100.00%
Business acquisition, goodwill		$ 35,431,000
Business acquisition, total purchase price consideration		67,223,000
Business acquisition, cash acquired		3,300,000
Net sales, included in consolidated statement of operations						30,000,000
Estimated contingent payments		7,982,000				8,200,000
Business combination maximum contingent consideration payment		$ 11,700,000
Business combination sales thresholds achievement maturity date		2020-12
Payment to former shareholder						1,500,000
MAS Automotive Distribution Inc [Member] | Selling, General and Administrative Expeses [Member]
Business Acquisition [Line Items]
Estimated contingent payments						$ 200,000

Business Acquisitions and Inv_4

Business Acquisitions and Investments - Summary of Preliminary Fair Value of Total Consideration (Detail) - USD ($) $ in Thousands	Oct. 26, 2017	Sep. 29, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Cash consideration (net of $3.3 million cash acquired)		$ 28,040	$ 3,128
MAS Automotive Distribution Inc [Member]
Business Acquisition [Line Items]
Cash consideration (net of $3.3 million cash acquired)	$ 56,859
Contingent cash consideration	7,982	$ 8,200
Seller liability assumed	896
Working capital adjustment	1,486
Total consideration assigned to net assets acquired	$ 67,223

Business Acquisitions and Inv_5

Business Acquisitions and Investments - Summary of Preliminary Fair Value of Total Consideration (Parenthetical) (Detail) $ in Millions	Oct. 26, 2017USD ($)
MAS Automotive Distribution Inc [Member]
Business Acquisition [Line Items]
Business acquisition, cash acquired	$ 3.3

Business Acquisitions and Inv_6

Business Acquisitions and Investments - Summary of Preliminary Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Sep. 29, 2018	Dec. 30, 2017	Oct. 26, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 80,065	$ 65,999		$ 28,146
MAS Automotive Distribution Inc [Member]
Business Acquisition [Line Items]
Current assets (net of $3.3 million cash acquired)			$ 21,846
Property, plant and equipment			1,615
Intangible assets			20,440
Goodwill			35,431
Total assets acquired			79,332
Current liabilities			5,641
Long-term liabilities			6,468
Total liabilities assumed			12,109
Net assets acquired			67,223
MAS Automotive Distribution Inc [Member] | As initially reported [Member]
Business Acquisition [Line Items]
Current assets (net of $3.3 million cash acquired)			21,756
Property, plant and equipment			1,615
Intangible assets			20,440
Goodwill			35,624
Total assets acquired			79,435
Current liabilities			5,691
Long-term liabilities			6,468
Total liabilities assumed			12,159
Net assets acquired			67,276
MAS Automotive Distribution Inc [Member] | Measurement period adjustments [Member]
Business Acquisition [Line Items]
Current assets (net of $3.3 million cash acquired)			90
Goodwill			(193)
Total assets acquired			(103)
Current liabilities			(50)
Total liabilities assumed			(50)
Net assets acquired			$ (53)

Business Acquisitions and Inv_7

Business Acquisitions and Investments - Summary of Preliminary Fair Values of Assets Acquired and Liabilities Assumed (Parenthetical) (Detail) $ in Millions	Oct. 26, 2017USD ($)
MAS Automotive Distribution Inc [Member]
Business Acquisition [Line Items]
Business acquisition, cash acquired	$ 3.3

Business Acquisitions and Inv_8

Business Acquisitions and Investments - Schedule of Valuation of Intangible Assets Acquired and Related Amortization Periods (Detail) - MAS Automotive Distribution Inc [Member] $ in Thousands	Oct. 26, 2017USD ($)
Business Acquisition [Line Items]
Valuation,Intangible assets	$ 20,440
Customer Relationships [Member]
Business Acquisition [Line Items]
Valuation,Intangible assets	$ 14,840
Customer Relationships [Member] | Minimum [Member]
Business Acquisition [Line Items]
Amortization Period (in years)	8 years
Customer Relationships [Member] | Maximum [Member]
Business Acquisition [Line Items]
Amortization Period (in years)	12 years
Tradenames [Member]
Business Acquisition [Line Items]
Valuation,Intangible assets	$ 5,600
Amortization Period (in years)	15 years

Business Acquisitions and Inv_9

Business Acquisitions and Investments - Schedule of Pro Forma Financial Information (Detail) - MAS Automotive Distribution Inc [Member] $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2017USD ($)$ / shares
Business Acquisition [Line Items]
Net sales	$ 702,811
Net income	$ 85,307
Diluted earnings per share | $ / shares	$ 2.49

Sales of Accounts Receivable -

Sales of Accounts Receivable - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Dec. 30, 2017
Receivables [Abstract]
Sale of accounts receivable	$ 438.6	$ 442.5
Additional receivables outstanding if receivables had not been sold	333.6		$ 380.8
Factoring costs associated with the sales of accounts receivable	$ 10	$ 8.4

Inventories - Inventories (Deta

Inventories - Inventories (Detail) - USD ($) $ in Thousands	Sep. 29, 2018	Dec. 30, 2017
Inventory Disclosure [Abstract]
Bulk product	$ 93,142	$ 82,010
Finished product	143,118	126,827
Packaging materials	3,697	3,312
Total	$ 239,957	$ 212,149

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Schedule of Goodwill (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 29, 2018	Dec. 30, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Balance at beginning of period	$ 65,999	$ 28,146
Goodwill acquired	14,368	37,853
Measurement period adjustments	(302)
Balance at end of period	$ 80,065	$ 65,999

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Schedule of Intangible Assets (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 29, 2018	Dec. 30, 2017
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 23,016	$ 23,016
Accumulated Amortization	2,309	858
Net Carrying Value	$ 20,707	22,158
Tradenames [Member]
Finite Lived Intangible Assets [Line Items]
Weighted Average Amortization Period	14 years 1 month 6 days
Gross Carrying Value	$ 5,600	5,600
Accumulated Amortization	373	62
Net Carrying Value	$ 5,227	5,538
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Weighted Average Amortization Period	9 years 6 months
Gross Carrying Value	$ 17,049	17,049
Accumulated Amortization	1,893	772
Net Carrying Value	$ 15,156	16,277
Technology [Member]
Finite Lived Intangible Assets [Line Items]
Weighted Average Amortization Period	13 years 3 months 18 days
Gross Carrying Value	$ 367	367
Accumulated Amortization	43	24
Net Carrying Value	$ 324	$ 343

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017
Finite Lived Intangible Assets [Line Items]
Amortization expense	$ 1.6
Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Amortization expense		$ 0.1

Revenue Recognition - Additiona

Revenue Recognition - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 29, 2018	Dec. 30, 2017
Revenue From Contract With Customer [Abstract]
Maximum credit terms allow to customers	1 year
Revenue, performance obligation, description of payment terms	A receivable is recorded when our right to consideration is unconditional and only the passage of time is required before payment of that consideration is due.
Contract assets	$ 0	$ 0
Contract liabilities	$ 0	$ 0

Revenue Recognition - Summary o

Revenue Recognition - Summary of Disaggregated Net Sales (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Net Sales	$ 247,954	$ 224,615	$ 713,363	$ 675,502
U.S. Customers [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	229,761	210,347	663,212	634,422
Non-U.S. Customers [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	18,193	14,268	50,151	41,080
Powertrain [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	100,994	94,177	295,363	284,393
Chassis [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	69,214	57,281	206,483	173,498
Automotive Body [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	67,000	62,791	179,539	185,804
Hardware [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	$ 10,746	$ 10,366	$ 31,978	$ 31,807

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	May 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized number of common stock shares for grant	1,200,000
Date of plan approval	May 16, 2018
Maximum grant period from date of plan approval	10 years
Shares available for grant under the plan	1,184,305
Compensation cost related to restricted stock	$ 2,500,000	$ 2,100,000
Compensation cost related to stock options	$ 400,000	200,000
Stock options granted	69,014
Stock options exercised	4,000
Cash received from stock option exercises under the plan	$ 0	100,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized number of common stock shares for grant			1,000,000
Number of shares purchased	7,382
Compensation cost	$ 200,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to non-vested stock options	$ 5,200,000
Unrecognized compensation cost related to nonvested stock options, weighted-average period	2 years 3 months 18 days
Tax benefit generated from compensation cost and credited		300,000
Restricted Stock [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Tax benefit generated from compensation cost and credited	$ 100,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to non-vested stock options	$ 1,600,000
Unrecognized compensation cost related to nonvested stock options, weighted-average period	2 years 10 months 24 days
Tax benefit generated from compensation cost and credited	$ 0	600,000
Capitalized compensation cost	$ 0	$ 0
Stock options granted	69,014	58,024
Stock options exercised	4,000	32,000

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Restricted Stock Activity (Detail)	9 Months Ended
	Sep. 29, 2018$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning Balance, Shares | shares	153,727
Granted, Shares | shares	80,872
Vested, Shares | shares	(38,631)
Cancelled, Shares | shares	(6,237)
Ending Balance, Shares | shares	189,731
Beginning Balance, Weighted Average Price | $ / shares	$ 59.96
Granted, Weighted Average Price | $ / shares	72.19
Vested, Weighted Average Price | $ / shares	61.07
Cancelled, Weighted Average Price | $ / shares	75.59
Ending Balance, Weighted Average Price | $ / shares	$ 64.43

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock Option Activity (Detail)	9 Months Ended
	Sep. 29, 2018USD ($)$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning Balance, Shares | shares	122,547
Granted, Shares | shares	69,014
Exercised, Shares | shares	(4,000)
Ending Balance, Shares | shares	187,561
Options Exercisable, Shares | shares	47,079
Beginning Balance, Weighted Average Exercise Price | $ / shares	$ 57.74
Granted, Weighted Average Exercise Price | $ / shares	72.32
Exercised, Weighted Average Exercise Price | $ / shares	5.67
Ending Balance, Weighted Average Exercise Price | $ / shares	64.21
Options Exercisable, Weighted Average Exercise Price | $ / shares	$ 51.55
Ending Balance, Weighted Average Remaining Terms (years)	3 years 8 months 12 days
Options Exercisable, Weighted Average Remaining Terms (years)	2 years 7 months 6 days
Ending Balance, Aggregate Intrinsic Value | $	$ 2,490,355
Options Exercisable, Aggregate Intrinsic Value | $	$ 1,220,858

Earnings Per Share - Additional

Earnings Per Share - Additional Information (Detail) - shares	9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Stock-based awards considered as anti-dilutive	63,000	47,500

Earnings Per Share - Schedule o

Earnings Per Share - Schedule of Computation of Basic Earnings per Share and Diluted Earnings per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Numerator
Net income	$ 34,017	$ 27,008	$ 99,003	$ 84,632
Denominator:
Weighted average basic shares outstanding	32,985	33,822	33,177	34,111
Effect of stock-based compensation awards	110	87	90	91
Weighted average diluted shares outstanding	33,095	33,909	33,267	34,202
Earnings Per Share:
Basic	$ 1.03	$ 0.80	$ 2.98	$ 2.48
Diluted	$ 1.03	$ 0.80	$ 2.98	$ 2.47

Common Stock Repurchases - Addi

Common Stock Repurchases - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 29, 2018	Dec. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchased and cancelled shares	20,160	19,110
Common stock repurchased, value	$ 1,500,000	$ 1,400,000
Common stock repurchased, average price	$ 73.35	$ 73.34
Share Repurchase Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchased and cancelled shares	486,487	1,006,365
Common stock repurchased, value	$ 33,800,000	$ 74,700,000
Common stock repurchased, average price	$ 69.41	$ 74.26
Share repurchase program shares authorized to be repurchased	$ 250,000,000

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 29, 2018USD ($)Supplier	Dec. 29, 2018USD ($)	Dec. 30, 2017USD ($)
Related Party Transaction [Line Items]
Rental payments based upon the terms of the lease			$ 1.6
Lease expiration date	Dec. 31, 2022
Joint Venture [Member]
Related Party Transaction [Line Items]
Minority interests in number of suppliers | Supplier	2
Joint Venture [Member] | Selling, General and Administrative Expeses [Member]
Related Party Transaction [Line Items]
Impairment charge	$ 1.1
Canada [Member]
Related Party Transaction [Line Items]
Rental payments based upon the terms of the lease			$ 0.1
Lease expiration date	Jan. 31, 2019
Scenario, Forecast [Member]
Related Party Transaction [Line Items]
Rental payments based upon the terms of the lease		$ 1.6
Scenario, Forecast [Member] | Canada [Member]
Related Party Transaction [Line Items]
Rental payments based upon the terms of the lease		$ 0.5

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 30, 2017	Sep. 29, 2018	Dec. 30, 2017
Income Tax Disclosure [Abstract]
Net unrecognized tax benefits		$ 2,500,000
Unrecognized tax benefits which would impact effective tax rate if recognized		2,200,000
Accrued interest and penalties related to uncertain tax positions		$ 700,000
U.S. corporate income tax rate		21.00%	35.00%
Net tax expense due to TCJA	$ 4,400,000
Adjustment to provisional expense due to TCJA		$ 0