Littelfuse (LFUS) 10-Q 30 Oct 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 28, 2019	Oct. 25, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 28, 2019
Document Transition Report	false
Entity File Number	0-20388
Entity Registrant Name	LITTELFUSE INC /DE
Entity Central Index Key	0000889331
Current Fiscal Year End Date	--12-29
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-3795742
Entity Address, Address Line One	8755 West Higgins Road
Entity Address, Address Line Two	Suite 500
Entity Address, City or Town	Chicago
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60631
City Area Code	773
Local Phone Number	628-1000
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	LFUS
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		24,358,002

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 29, 2018
Current assets:
Cash and cash equivalents	$ 476,057	$ 489,733
Short-term investments	33	34
Trade receivables, less allowances of $39,874 and $36,038 at September 28, 2019 and December 29, 2018, respectively	226,352	232,892
Inventories	240,059	258,228
Prepaid income taxes and income taxes receivable	2,730	2,339
Prepaid expenses and other current assets	62,361	49,291
Total current assets	1,007,592	1,032,517
Net property, plant, and equipment	329,792	339,894
Intangible assets, net of amortization	326,417	361,474
Goodwill	813,653	826,715
Investments	26,662	25,405
Deferred income taxes	7,485	7,330
Right of use lease assets, net	21,598
Other assets	18,162	20,971
Total assets	2,551,361	2,614,306
Current liabilities:
Accounts payable	107,211	126,323
Accrued liabilities	114,549	138,405
Accrued income taxes	16,989	20,547
Current portion of long-term debt	10,000	10,000
Total current liabilities	248,749	295,275
Long-term debt, less current portion	668,160	684,730
Deferred income taxes	51,776	51,853
Accrued post-retirement benefits	28,725	31,874
Non-current operating lease liabilities	17,237
Other long-term liabilities	64,502	72,232
Shareholders’ equity:
Common stock, par value $0.01 per share: 34,000,000 shares authorized; shares issued, September 28, 2019–25,820,918; December 29, 2018–25,641,959	256	254
Treasury stock, at cost: 1,473,558 and 868,045 shares, respectively	(216,384)	(116,454)
Additional paid-in capital	860,871	835,828
Accumulated other comprehensive loss	(112,608)	(97,924)
Retained earnings	939,946	856,507
Littelfuse, Inc. shareholders’ equity	1,472,081	1,478,211
Non-controlling interest	131	131
Total equity	1,472,212	1,478,342
Total liabilities and equity	$ 2,551,361	$ 2,614,306

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 29, 2018
Statement of Financial Position [Abstract]
Allowance for trade receivables	$ 39,874	$ 36,038
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock authorized (in shares)	34,000,000	34,000,000
Common stock issued (in shares)	25,820,918	25,641,959
Treasury stock (in shares)	1,473,558	868,045

Condensed Consolidated Statemen

Condensed Consolidated Statements of Net Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Income Statement [Abstract]
Net sales	$ 361,971	$ 439,191	$ 1,165,350	$ 1,316,187
Cost of sales	231,025	259,597	737,368	817,983
Gross profit	130,946	179,594	427,982	498,204
Selling, general, and administrative expenses	54,224	69,782	174,845	220,540
Research and development expenses	19,728	20,454	62,595	65,742
Amortization of intangibles	9,827	13,130	30,068	38,501
Total operating expenses	83,779	103,366	267,508	324,783
Operating income	47,167	76,228	160,474	173,421
Interest expense	5,559	5,775	16,834	16,980
Foreign exchange loss (gain)	4,968	982	5,636	(6,372)
Other (income) expense, net	(4,764)	1,259	(3,406)	(2,362)
Income before income taxes	41,404	68,212	141,410	165,175
Income taxes	5,757	14,666	24,982	33,275
Net income	$ 35,647	$ 53,546	$ 116,428	$ 131,900
Income per share:
Basic (in dollars per share)	$ 1.46	$ 2.13	$ 4.72	$ 5.31
Diluted (in dollars per share)	$ 1.44	$ 2.10	$ 4.68	$ 5.23
Weighted-average shares and equivalent shares outstanding:
Basic (in shares)	24,482	25,109	24,646	24,817
Diluted (in shares)	24,684	25,471	24,894	25,212

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 35,647	$ 53,546	$ 116,428	$ 131,900
Other comprehensive income (loss):
Pension and postemployment adjustment, net of tax	137	(115)	249	648
Foreign currency translation adjustments	(17,163)	(7,832)	(14,933)	(24,816)
Comprehensive income	$ 18,621	$ 45,599	$ 101,744	$ 107,732

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018
OPERATING ACTIVITIES
Net income	$ 116,428	$ 131,900
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	38,988	37,559
Amortization of intangibles	30,068	38,501
Deferred revenue	(228)	3,965
Non-cash inventory charges	0	36,927
Impairment charges	322	1,125
Stock-based compensation	15,738	23,153
Loss (gain) on investments and other assets	559	(350)
Deferred income taxes	(203)	(10,979)
Other	8,267	594
Changes in operating assets and liabilities:
Trade receivables	2,781	(20,588)
Inventories	18,102	(17,624)
Accounts payable	(29,453)	17,033
Accrued liabilities and income taxes	(44,241)	20,736
Prepaid expenses and other assets	3,735	(9,836)
Net cash provided by operating activities	160,863	252,116
INVESTING ACTIVITIES
Acquisitions of businesses, net of cash acquired	(775)	(313,475)
Purchases of property, plant, and equipment	(38,397)	(55,946)
Net proceeds from sale of property, plant and equipment, and other	6,212	858
Net cash used in investing activities	(32,960)	(368,563)
FINANCING ACTIVITIES
Proceeds of revolving credit facility	0	60,000
Proceeds of term loan	0	75,000
Net proceeds from senior notes payable	0	175,000
Payments of term loan	(7,500)	(42,525)
Payments of revolving credit facility	0	(60,000)
Net proceeds related to stock-based award activities	4,412	17,920
Purchases of common stock	(99,387)	0
Debt issuance costs	0	(878)
Cash dividends paid	(32,990)	(29,258)
Net cash (used in) provided by financing activities	(135,465)	195,259
Effect of exchange rate changes on cash and cash equivalents	(6,114)	(10,273)
(Decrease) increase in cash and cash equivalents	(13,676)	68,539
Cash and cash equivalents at beginning of period	489,733	429,676
Cash and cash equivalents at beginning of period	476,057	498,215
Supplementary Cash Flow Information
Cash paid during the period for interest	17,872	15,785
Capital expenditures, not yet paid	$ 8,978	$ 0

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Addl. Paid in Capital	Treasury Stock	Accum. Other Comp. Inc. (Loss)	Retained Earnings	Non- controlling Interest
Balance at Dec. 30, 2017	$ 927,556	$ 229	$ 310,012	$ (41,294)	$ (63,668)	$ 722,140	$ 137
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	36,029					36,029
Cumulative effect adjustment	0				(9,795)	9,795
Other comprehensive income (loss), net of tax	(279)				(279)
Stock-based compensation	8,714		8,714
Withheld shares on restricted share units for withholding taxes	(2,758)			(2,758)
Stock options exercised	9,609		9,609
Issuance of common stock	472,301	22	472,279
Cash dividends paid	(9,198)					(9,198)
Balance at Mar. 31, 2018	1,441,974	251	800,614	(44,052)	(73,742)	758,766	137
Balance at Dec. 30, 2017	927,556	229	310,012	(41,294)	(63,668)	722,140	137
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	131,900
Other comprehensive income (loss), net of tax	(24,168)
Balance at Sep. 29, 2018	1,519,396	254	830,612	(48,546)	(97,631)	834,577	130
Balance at Mar. 31, 2018	1,441,974	251	800,614	(44,052)	(73,742)	758,766	137
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	42,326					42,326
Other comprehensive income (loss), net of tax	(15,942)				(15,942)
Stock-based compensation	7,169		7,169
Non-controlling interest	(7)						(7)
Withheld shares on restricted share units for withholding taxes	(4,284)			(4,284)
Stock options exercised	8,045	2	8,043
Cash dividends paid	(9,261)					(9,261)
Balance at Jun. 30, 2018	1,470,020	253	815,826	(48,336)	(89,684)	791,831	130
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	53,546					53,546
Other comprehensive income (loss), net of tax	(7,947)				(7,947)
Stock-based compensation	7,270		7,270
Withheld shares on restricted share units for withholding taxes	(210)			(210)
Stock options exercised	7,517	1	7,516
Cash dividends paid	(10,800)					(10,800)
Balance at Sep. 29, 2018	1,519,396	254	830,612	(48,546)	(97,631)	834,577	130
Balance at Dec. 29, 2018	1,478,342	254	835,828	(116,454)	(97,924)	856,507	131
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	36,989					36,989
Other comprehensive income (loss), net of tax	8,073				8,073
Stock-based compensation	3,966		3,966
Withheld shares on restricted share units for withholding taxes	(94)			(94)
Stock options exercised	2,292		2,292
Repurchases of common stock	(13,555)			(13,555)
Cash dividends paid	(10,625)					(10,625)
Balance at Mar. 30, 2019	1,505,388	254	842,086	(130,103)	(89,851)	882,871	131
Balance at Dec. 29, 2018	1,478,342	254	835,828	(116,454)	(97,924)	856,507	131
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	116,428
Other comprehensive income (loss), net of tax	(14,684)
Balance at Sep. 28, 2019	1,472,212	256	860,871	(216,384)	(112,608)	939,946	131
Balance at Mar. 30, 2019	1,505,388	254	842,086	(130,103)	(89,851)	882,871	131
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	43,792					43,792
Other comprehensive income (loss), net of tax	(5,731)				(5,731)
Stock-based compensation	8,284		8,284
Withheld shares on restricted share units for withholding taxes	(4,010)			(4,010)
Stock options exercised	4,823	1	4,822
Repurchases of common stock	(31,955)			(31,955)
Cash dividends paid	(10,649)					(10,649)
Balance at Jun. 29, 2019	1,509,942	255	855,192	(166,068)	(95,582)	916,014	131
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	35,647					35,647
Other comprehensive income (loss), net of tax	(17,026)				(17,026)
Stock-based compensation	3,488		3,488
Withheld shares on restricted share units for withholding taxes	(790)			(790)
Stock options exercised	2,192	1	2,191
Repurchases of common stock	(49,526)			(49,526)
Cash dividends paid	(11,715)					(11,715)
Balance at Sep. 28, 2019	$ 1,472,212	$ 256	$ 860,871	$ (216,384)	$ (112,608)	$ 939,946	$ 131

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Stockholders' Equity (Parentheticals) - $ / shares	3 Months Ended
	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018
Statement of Stockholders' Equity [Abstract]
Cash dividends paid, per share (in dollars per share)	$ 0.48	$ 0.43	$ 0.43	$ 0.43	$ 0.37	$ 0.37

Summary of Significant Accounti

Summary of Significant Accounting Policies and Other Information	9 Months Ended
	Sep. 28, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies and Other Information	Summary of Significant Accounting Policies and Other Information Nature of Operations Littelfuse, Inc. and subsidiaries (the “Company”) is a global manufacturer of leading technologies in circuit protection, power control and sensing. The Company's products are found in automotive and commercial vehicles, industrial applications, data and telecommunications, medical devices, consumer electronics and appliances. With its broad product portfolio of fuses, semiconductors, polymers, ceramics, relays and sensors, and extensive global infrastructure, the Company’s worldwide associates partner with its customers to design, manufacture and deliver innovative, high-quality solutions for a safer, greener and increasingly connected world. Basis of Presentation The Company’s accompanying unaudited Condensed Consolidated Financial Statements have been prepared in accordance with U.S. Generally Accepted Accounting Principles (“GAAP”) for interim financial information, the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, certain information and disclosures normally included in the consolidated balance sheets, statements of net income and comprehensive income, statements of cash flows, and statement of stockholders' equity prepared in conformity with U.S. GAAP have been condensed or omitted as permitted by such rules and regulations, although the Company believes that the disclosures made are adequate to make the information not misleading. They have been prepared in accordance with accounting policies described in the Company’s Annual Report on Form 10-K for the fiscal year ended December 29, 2018 which should be read in conjunction with the disclosures therein. In the opinion of management, all adjustments considered necessary for a fair presentation have been included and are of a normal, recurring nature. Operating results for interim periods are not necessarily indicative of annual operating results. Revenue Recognition On December 31, 2017, the Company adopted new guidance on revenue from contracts with customers using the modified retrospective method. The adoption did not have a significant impact on the Company’s consolidated financial statements. Revenue Disaggregation The following tables disaggregate the Company’s revenue by primary business units for the three and nine months ended September 28, 2019 and September 29, 2018 : Three Months Ended September 28, 2019 Nine Months Ended September 28, 2019 (in thousands) Electronics Segment Automotive Segment Industrial Segment Total Electronics Segment Automotive Segment Industrial Segment Total Electronics – Passive Products and Sensors $ 94,766 $ — $ — $ 94,766 $ 311,624 $ — $ — $ 311,624 Electronics – Semiconductor 132,486 — — 132,486 440,575 — — 440,575 Passenger Car Products — 53,889 — 53,889 — 164,348 — 164,348 Automotive Sensors — 23,877 — 23,877 — 74,616 — 74,616 Commercial Vehicle Products — 26,915 — 26,915 — 87,850 — 87,850 Industrial Products — — 30,038 30,038 — — 86,337 86,337 Total $ 227,252 $ 104,681 $ 30,038 $ 361,971 $ 752,199 $ 326,814 $ 86,337 $ 1,165,350 Three Months Ended September 29, 2018 Nine Months Ended September 29, 2018 (in thousands) Electronics Segment Automotive Segment Industrial Segment Total Electronics Segment Automotive Segment Industrial Segment Total Electronics – Passive Products and Sensors $ 124,174 $ — $ — $ 124,174 $ 366,990 $ — $ — $ 366,990 Electronics – Semiconductor 172,298 — — 172,298 493,250 — — 493,250 Passenger Car Products — 57,761 — 57,761 — 184,922 — 184,922 Automotive Sensors — 27,311 — 27,311 — 89,362 — 89,362 Commercial Vehicle Products — 29,344 — 29,344 — 93,434 — 93,434 Industrial Products — — 28,303 28,303 — — 88,229 88,229 Total $ 296,472 $ 114,416 $ 28,303 $ 439,191 $ 860,240 $ 367,718 $ 88,229 $ 1,316,187 See Note 16, Segment Information for net sales by segment and countries. Revenue Recognition The Company recognizes revenue on product sales in the period in which the Company satisfies its performance obligation and control of the product is transferred to the customer. The Company’s sales arrangements with customers are predominately short term in nature and generally provide for transfer of control at the time of shipment as this is the point at which title and risk of loss of the product transfers to the customer. At the end of each period, for those shipments where title to the products and the risk of loss and rewards of ownership do not transfer until the product has been received by the customer, the Company adjusts revenues and cost of sales for the delay between the time that the products are shipped and when they are received by the customer. The amount of revenue recorded reflects the consideration to which the Company expects to be entitled in exchange for goods and may include adjustments for customer allowance, rebates and price adjustments. The Company’s distribution channels are primarily through direct sales and independent third-party distributors. The Company elected the practical expedient under Accounting Standards Codification ("ASC") 340-40-25-4 to expense commissions when incurred as the amortization period of the commission asset the Company would have otherwise recognized is less than one year. Revenue and Billing The Company generally accepts orders from customers through receipt of purchase orders or electronic data interchange based on written sales agreements and purchasing contracts. Contract pricing and selling agreement terms are based on market factors, costs, and competition. Pricing is often negotiated as an adjustment (premium or discount) from the Company’s published price lists. The customer is invoiced when the Company’s products are shipped to them in accordance with the terms of the sales agreement. As the Company’s standard payment terms are less than one year, the Company elected the practical expedient under ASC 606-10-32-18 to not assess whether a contract has a significant financing component. The Company also elected the practical expedient provided in ASC 606-10-25-18B to treat all product shipping and handling activities as fulfillment activities, and therefore recognize the gross revenue associated with the contract, inclusive of any shipping and handling revenue. This is similar to the Company’s prior practice and therefore the effect of the new guidance is immaterial. Ship and Debit Program Some of the terms of the Company’s sales agreements and normal business conditions provide customers (distributors) the ability to receive price adjustments on products previously shipped and invoiced. This practice is common in the industry and is referred to as a “ship and debit” program. This program allows the distributor to debit the Company for the difference between the distributors’ contracted price and a lower price for specific transactions. Under certain circumstances (usually in a competitive situation or large volume opportunity), a distributor will request authorization for pricing allowances to reduce its price. When the Company approves such a reduction, the distributor is authorized to “debit” its account for the difference between the contracted price and the lower approved price. The Company establishes reserves for this program based on historic activity and actual authorizations for the debit and recognizes these debits as a reduction of revenue. Return to Stock The Company has a return to stock policy whereby certain customers, with prior authorization from Littelfuse management, can return previously purchased goods for full or partial credit. The Company establishes an estimated allowance for these returns based on historic activity. Sales revenue and cost of sales are reduced to anticipate estimated returns. Volume Rebates The Company offers volume based sales incentives to certain customers to encourage greater product sales. If customers achieve their specific quarterly or annual sales targets, they are entitled to rebates. The Company estimates the projected amount of rebates that will be achieved by the customer and recognizes this estimated cost as a reduction to revenue as products are sold. Recently Adopted Accounting Standards In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, "Leases" (Topic 842), ("ASC 842"). This ASU requires lessees to recognize, on the balance sheet, assets and liabilities for the rights and obligations created by leases of greater than twelve months. The accounting by lessors will remain largely unchanged. The ASU is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. Adoption requires using a modified retrospective transition with either 1) periods prior to the adoption date being recast or 2) a cumulative-effect adjustment recognized to the opening balance of retained earnings on the adoption date with prior periods not recast. The Company adopted the standard on December 30, 2018 using alternative modified retrospective transition method provided in ASU No. 2018-11, "Leases (Topic 842): Target Improvements." Under this method, the Company recorded a cumulative-effect adjustment as of December 30, 2018 and did not record any retrospective adjustments to comparative periods to reflect the adoption of ASC 842. The new standard provides a number of optional practical expedients in transition. The Company has elected the ‘package of practical expedients’ which permits us not to reassess under the new standard our prior conclusions about lease identification, lease classification and initial direct costs. The Company has not elected the use-of-hindsight. Adoption of ASC 842 resulted in the recognition of operating lease right-of-use assets ("ROU") net of deferred rent of $26.1 million and lease liabilities of $29.4 million , as of December 30, 2018 for operating leases on its Condensed Consolidated Balance Sheets, with no impact to its Condensed Consolidated Statements of Net Income and no impact on Condensed Consolidated Statements of Cash Flow. See Note 6, Lease Commitments, for further discussion. In February 2018, the FASB issued ASU No. 2018-02 “Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income,” which permits the reclassification of tax effects stranded in accumulated other comprehensive income to retained earnings as a result of the Tax Act. The standard also requires entities to disclose whether or not they elected to reclassify the tax effects related to the Tax Act as well as their policy for releasing income tax effects from accumulated other comprehensive income. The standard allows the option of applying either a retrospective adoption, meaning the standard is applied to all periods in which the effect of the Tax Act is recognized, or applying the amendments in the period of adoption, meaning an adjustment is made to shareholder’s equity as of the beginning of the reporting period. The Company adopted the new standard on December 30, 2018. The adoption of this guidance did not have a material effect on our Condensed Consolidated Financial Statements.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 28, 2019
Business Combinations [Abstract]
Acquisitions	Acquisitions The Company accounts for acquisitions using the acquisition method in accordance with ASC 805, “Business Combinations,” in which assets acquired and liabilities assumed are recorded at fair value as of the date of acquisition. The operating results of the acquired business are included in the Company’s Consolidated Financial Statements from the date of the acquisition. IXYS Corporation On January 17, 2018, the Company acquired IXYS Corporation (“IXYS”), a global pioneer in the power semiconductor and integrated circuit markets with a focus on medium to high voltage power control semiconductors across the industrial, communications, consumer and medical markets. IXYS has a broad customer base, serving more than 3,500 customers through its direct sales force and global distribution partners. The acquisition of IXYS is expected to accelerate the Company’s growth across the power control market driven by IXYS’s extensive power semiconductor portfolio and technology expertise. With IXYS, the Company will be able to diversify and expand its presence within industrial electronics markets, leveraging the strong IXYS industrial OEM customer base. The Company also expects to increase long-term penetration of its power semiconductor portfolio in automotive markets, expanding its global content per vehicle. Upon completion of the acquisition, at IXYS stockholders’ election and subject to proration, each share of IXYS common stock, par value $0.01 per share, owned immediately prior to the effective time was canceled and extinguished and automatically converted into the right to receive: (i) $23.00 in cash (subject to applicable withholding tax), without interest (referred to as the cash consideration), or (ii) 0.1265 of a share of common stock, par value $0.01 per share, of Littelfuse (referred to as the stock consideration). IXYS stockholders received cash in lieu of any fractional shares of Littelfuse common stock that the IXYS stockholders would otherwise have been entitled to receive. Additionally, each outstanding option to purchase shares of IXYS common stock granted under an IXYS equity plan were assumed by Littelfuse and converted into an option to acquire (i) a number of shares of Littelfuse common stock equal to the number of shares of IXYS common stock subject to such option immediately prior to the effective time multiplied by 0.1265 , rounded down to the nearest whole share, with (ii) an exercise price per share of Littelfuse common stock equal to the exercise price of such IXYS stock option immediately prior to the effective time divided by 0.1265 , rounded up to the nearest whole cent. Based on the $207.5 per share opening price of Littelfuse common stock on January 17, 2018, the consideration IXYS stockholders received in exchange of their IXYS common stock in the acquisition had a value of $814.8 million comprised of $380.6 million of cash and $434.2 million of Littelfuse stock. In addition to the consideration transferred related to IXYS common stock, the value of consideration transferred, and included in the purchase price, related to IXYS stock options that were converted to Littelfuse stock options, or cash settled, had a value of $41.7 million . As a result, total consideration was valued at $856.5 million . The total purchase price of $856.5 million has been allocated to assets acquired and liabilities assumed, as of the completion of the acquisition, based on estimated fair values. The following table summarizes the purchase price allocation of the fair value of assets acquired and liabilities assumed in the IXYS acquisition: (in thousands) Purchase Price Allocation Total purchase consideration: Cash, net of cash acquired $ 302,865 Cash settled stock options 3,622 Littelfuse stock 434,192 Converted stock options 38,109 Total purchase consideration $ 778,788 Allocation of consideration to assets acquired and liabilities assumed: Current assets, net $ 155,930 Property, plant, and equipment 77,442 Intangible assets 212,720 Goodwill 382,360 Other non-current assets 28,706 Other non-current liabilities (78,370 ) $ 778,788 Approximately $49.1 million of net receivables was included in IXYS’s current assets. All IXYS goodwill, other assets and liabilities were recorded in the Electronics segment and primarily reflected in the Americas and European geographic areas. The goodwill resulting from this acquisition consists largely of the Company’s expected future product sales and synergies from combining IXYS’s products and technology with the Company’s existing electronics product portfolio. Goodwill resulting from the IXYS acquisition is not expected to be deductible for tax purposes. Included in the Company’s Condensed Consolidated Statements of Net Income for the three and nine months ended September 29, 2018 are net sales of approximately $99.7 million and $286.2 million , respectively, and an income (loss) before income taxes of $6.2 million and $(25.5) million , respectively, since the January 17, 2018 acquisition of IXYS. The Company recognized approximately $4.3 million and $11.8 million of stock compensation expense related to IXYS stock options converted to Littelfuse stock options during the three and nine months ended September 29, 2018 , of which $4.5 million was recognized immediately as it related to prior services periods. As required by purchase accounting rules, the Company recorded a $36.9 million step-up of inventory to its fair value as of the acquisition date based on the valuation. The step-up was fully amortized as a non-cash charge to cost of goods sold during the first and second quarters of 2018, as the acquired inventory was sold, and reflected as other non-segment costs. During the nine months ended September 29, 2018 , the Company incurred approximately $11.0 million of legal and professional fees related to this acquisition which were primarily recognized as selling, general, and administrative expenses . These costs were reflected as other non-segment costs. Pro Forma Results The following table summarizes, on a pro forma basis, the combined results of operations of the Company and IXYS as though the acquisition had occurred as of January 1, 2017. The pro forma amounts presented are not necessarily indicative of either the actual consolidated results had the IXYS acquisition occurred as of January 1, 2017 or of future consolidated operating results. Three Months Ended Nine Months Ended (in thousands, except per share amounts) September 29, 2018 September 29, 2018 Net sales $ 439,191 $ 1,332,900 Income before income taxes 71,737 228,503 Net income 56,060 179,264 Net income per share — basic 2.23 7.17 Net income per share — diluted 2.18 7.16 Pro forma results presented above primarily reflect the following adjustments: Three Months Ended Nine Months Ended (in thousands) September 29, 2018 September 29, 2018 Amortization(a) $ 3,104 $ 8,289 Transaction costs(b) — 9,976 Amortization of inventory step-up(c) — 36,927 Stock compensation(d) 421 5,110 Income tax impact of above items (1,011 ) (14,290 ) (a) The amortization adjustment for the three and nine months ended September 29, 2018 primarily reflects the reduction of amortization expense in the period related to the Order backlog intangible asset. The Order backlog has a useful life of twelve months and was fully amortized in the fiscal 2017 pro forma results. (b) The transaction cost adjustments reflect the reversal of certain bank and attorney fees from the nine months ended September 29, 2018 and recognition of those fees during the nine months ended September 30, 2017. (c) The amortization of inventory step-up adjustment reflects the reversal of the amount recognized during the three and nine months ended September 29, 2018 and recognition of those costs during the three and nine months ended September 30, 2017. The inventory step-up was amortized over five months as the inventory was sold. (d) The stock compensation adjustment reflects the reversal of the portion of stock compensation for IXYS stock options that were converted to Littelfuse stock options and expensed immediately during the nine months ended September 29, 2018

Inventories

Inventories	9 Months Ended
	Sep. 28, 2019
Inventory Disclosure [Abstract]
Inventories	Inventories The components of inventories at September 28, 2019 and December 29, 2018 are as follows: (in thousands) September 28, 2019 December 29, 2018 Raw materials $ 71,327 $ 69,883 Work in process 78,022 88,505 Finished goods 90,710 99,840 Total $ 240,059 $ 258,228

Property, Plant, and Equipment

Property, Plant, and Equipment	9 Months Ended
	Sep. 28, 2019
Property, Plant and Equipment [Abstract]
Property, Plant, and Equipment	Property, Plant, and Equipment The components of net property, plant, and equipment at September 28, 2019 and December 29, 2018 are as follows: (in thousands) September 28, 2019 December 29, 2018 Land $ 24,699 $ 25,630 Building 106,062 114,636 Equipment 605,965 583,043 Accumulated depreciation and amortization (406,934 ) (383,415 ) Total $ 329,792 $ 339,894 The Company recorded depreciation expense of $13.3 million and $13.1 million for the three months ended September 28, 2019 and September 29, 2018 , respectively, and $39.0 million and $37.6 million for the nine months ended September 28, 2019 and September 29, 2018

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	9 Months Ended
	Sep. 28, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets The amounts for goodwill and changes in the carrying value by segment for the nine months ended September 28, 2019 are as follows: (in thousands) Electronics Automotive Industrial Total As of December 29, 2018 $ 656,039 $ 132,332 $ 38,344 $ 826,715 Currency translation (10,627 ) (2,530 ) 95 (13,062 ) As of September 28, 2019 $ 645,412 $ 129,802 $ 38,439 $ 813,653 The components of other intangible assets at September 28, 2019 are as follows: (in thousands) Gross Carrying Value Accumulated Amortization Net Book Value Patents, licenses and software $ 136,565 $ 76,797 $ 59,768 Distribution network 43,638 36,014 7,624 Customer relationships, trademarks, and tradenames 372,627 113,602 259,025 Total $ 552,830 $ 226,413 $ 326,417 During the three months ended September 28, 2019 and September 29, 2018 , the Company recorded amortization expense of $9.8 million and $13.1 million , respectively. During the nine months ended September 28, 2019 and September 29, 2018 , the Company recorded amortization expense of $30.1 million and $38.5 million , respectively. Estimated annual amortization expense related to intangible assets with definite lives as of September 28, 2019 is as follows: (in thousands) Amount 2019 $ 41,376 2020 39,206 2021 37,606 2022 36,532 2023 32,150 2024 and thereafter 169,616 Total $ 356,486

Lease Commitments

Lease Commitments	9 Months Ended
	Sep. 28, 2019
Leases [Abstract]
Lease Commitments	Lease Commitments The Company leases office and production space under various non-cancelable operating leases that expire no later than 2025. Certain real estate leases include one or more options to renew. The exercise of lease renewal options is at the Company's sole discretion. Options to extend the lease are included in the lease term when it is reasonably certain the Company will exercise the option. The Company also has production equipment, office equipment and vehicles under operating leases. The depreciable life of assets and leasehold improvements are limited by the expected lease term, unless there is a transfer of title or purchase option that is reasonably certain of exercise. Certain leases include rental payments adjusted periodically for inflation. The lease agreements do not contain any material residual value guarantee or material restrictive covenants. The Company does not have a published credit rating because it has no publicly traded debt; therefore, the Company is generating its incremental borrowing rate (IBR), using a synthetic credit rating model that compares its credit quality to other rated companies based on certain financial metrics and ratios. The reference rate will be based on the yield curve of companies with similar credit quality based on the metrics and adjusted for currency in regions where we have significant operations. All leases with an initial term of 12 months or less that do not include an option to extend or purchase the underlying asset that the Company is reasonably certain to exercise (“short-term leases”) are not recorded on the Condensed Consolidated Balance Sheet. Short-term lease expenses are recognized on a straight-line basis over the lease term. The following table presents the classification of ROU assets and lease liabilities as of September 28, 2019 : Leases (in thousands) Condensed Consolidated Balance Sheet Classification September 28, 2019 Assets Operating ROU assets Right of use lease assets, net $ 21,598 Liabilities Current operating lease liabilities Accrued liabilities $ 6,926 Non-current operating lease liabilities Non-current operating lease liabilities 17,237 Total lease liabilities $ 24,163 The following table represents the lease costs for the three and nine months ended ended September 28, 2019 : Leases cost (in thousands) Condensed Consolidated Statements of Net Income Classification Three Months Ended September 28, 2019 Nine Months Ended Short-term lease expenses Cost of sales, SG&A expenses $ 86 $ 387 Variable lease expenses Cost of sales, SG&A expenses 239 621 Operating lease rent expenses Cost of sales, SG&A expenses 2,131 6,539 Total operating lease costs Cost of sales, SG&A expenses $ 2,456 $ 7,547 Maturity of Lease Liabilities as of September 28, 2019 (in thousands) Operating leases 2019 (excluding the nine months ended September 28, 2019) $ 2,155 2020 7,571 2021 5,878 2022 4,873 2023 3,252 2024 and thereafter 3,253 Total lease payments $ 26,982 Present value of lease liabilities $ 24,163 Operating Lease Term and Discount Rate September 28, 2019 Weighted-average remaining lease term (years) 4.19 Weighted-average discount rate 5.18 % Other Information (in thousands) Nine Months Ended Cash paid for amounts included in the measurement of lease liabilities Operating cash flow payments for operating leases $ (6,762 ) Leased assets obtained in exchange for operating lease liabilities 2,051

Accrued Liabilities

Accrued Liabilities	9 Months Ended
	Sep. 28, 2019
Payables and Accruals [Abstract]
Accrued Liabilities	Accrued Liabilities The components of accrued liabilities at September 28, 2019 and December 29, 2018 are as follows: (in thousands) September 28, 2019 December 29, 2018 Employee-related liabilities $ 42,076 $ 60,640 Other non-income taxes 32,453 21,523 Operating lease liability 6,926 — Professional services 4,117 6,169 Interest 3,239 5,137 Accrued share repurchases — 4,349 Restructuring liability 2,302 3,887 Other 23,436 36,700 Total $ 114,549 $ 138,405 Employee-related liabilities consist primarily of payroll, sales commissions, bonus, employee benefit accruals and workers’ compensation. Bonus accruals include amounts earned pursuant to the Company’s primary employee incentive compensation plans. Other accrued liabilities include miscellaneous operating accruals and other client-related liabilities.

Restructuring, Impairment and O

Restructuring, Impairment and Other Charges	9 Months Ended
	Sep. 28, 2019
Restructuring and Related Activities [Abstract]
Restructuring, Impairment and Other Charges	Restructuring, Impairment and Other Charges The Company recorded restructuring, impairment and other charges for the three and nine months ended September 28, 2019 and September 29, 2018 as follows: Three months ended September 28, 2019 Nine months ended September 28, 2019 (in thousands) Electronics Automotive Industrial Total Electronics Automotive Industrial Total Employee terminations $ 655 $ 109 $ 49 $ 813 $ 4,153 $ 3,955 $ 770 $ 8,878 Other restructuring charges 128 1,150 124 1,402 141 1,240 374 1,755 Total restructuring charges 783 1,259 173 2,215 4,294 5,195 1,144 10,633 Impairment — 322 — 322 — 322 — 322 Total $ 783 $ 1,581 $ 173 $ 2,537 $ 4,294 $ 5,517 $ 1,144 $ 10,955 Three months ended September 29, 2018 Nine months ended September 29, 2018 (in thousands) Electronics Automotive Industrial Total Electronics Automotive Industrial Total Employee terminations $ 4,614 $ 202 $ — $ 4,816 $ 7,693 $ 301 $ 65 $ 8,059 Other restructuring charges — 166 — 166 670 166 — 836 Total restructuring charges 4,614 368 — 4,982 8,363 467 65 8,895 Impairment — — — — — 88 1,037 1,125 Total $ 4,614 $ 368 $ — $ 4,982 $ 8,363 $ 555 $ 1,102 $ 10,020 2019 For the three and nine months ended September 28, 2019 , the Company recorded total restructuring charges of $2.2 million and $10.6 million , respectively, for employee termination costs and other restructuring charges. These charges primarily related to the reorganization of operations and selling, general and administrative functions as well as the integration of IXYS within the Electronics segment and the reorganization of operations in the automotive sensors and commercial vehicle products businesses within the Automotive segment. In April 2019, we announced the closure of a European manufacturing facility in the automotive sensors business within the Automotive segment. The Company recorded $1.7 million of employee termination costs and $1.1 million of other restructuring and impairment charges associated with this plant closure. 2018 For three and nine months ended September 29, 2018 , the Company recorded total restructuring charges of $5.0 million and $8.9 million , respectively, for employee termination costs and other restructuring charges related to lease termination and facility closure. These charges primarily related to the integration of IXYS and the reorganization of the IXYS Radio Pulse business within the Electronics segment. For the nine months ended September 29, 2018 , the Company recorded impairment charges of $1.1 million primarily related to the impairment of a building and a trade name associated with the exit of the Custom business within the Industrial segment. The restructuring reserves as of September 28, 2019 and December 29, 2018 are $2.3 million and $3.9 million , respectively. The restructuring reserves are included within accrued liabilities in the Condensed Consolidated Balance Sheets. The Company anticipates the remaining payments associated with employee terminations will primarily be completed by December 2019.

Debt

Debt	9 Months Ended
	Sep. 28, 2019
Debt Disclosure [Abstract]
Debt	Debt The carrying amounts of debt at September 28, 2019 and December 29, 2018 are as follows: (in thousands) September 28, December 29, Term Loan $ 147,500 $ 155,000 Euro Senior Notes, Series A due 2023 128,002 133,417 Euro Senior Notes, Series B due 2028 103,932 108,330 U.S. Senior Notes, Series A due 2022 25,000 25,000 U.S. Senior Notes, Series B due 2027 100,000 100,000 U.S. Senior Notes, Series A due 2025 50,000 50,000 U.S. Senior Notes, Series B due 2030 125,000 125,000 Other 2,619 2,619 Unamortized debt issuance costs (3,893 ) (4,636 ) Total debt 678,160 694,730 Less: Current maturities (10,000 ) (10,000 ) Total long-term debt $ 668,160 $ 684,730 Revolving Credit Facility / Term Loan On March 4, 2016, the Company entered into a five -year credit agreement (“Credit Agreement”) with a group of lenders for up to $700.0 million . The Credit Agreement consisted of an unsecured revolving credit facility (“Revolving Credit Facility”) of $575.0 million and an unsecured term loan credit facility (“Term Loan”) of up to $125.0 million . In addition, the Company had the ability, from time to time, to increase the size of the Revolving Credit Facility and the Term Loan by up to an additional $150.0 million , in the aggregate, in each case in minimum increments of $25.0 million , subject to certain conditions and the agreement of participating lenders. On October 13, 2017, the Company amended the Credit Agreement to increase the Revolving Credit Facility from $575.0 million to $700.0 million and increase the Term Loan from $125.0 million to $200.0 million and to extend the expiration date from March 4, 2021 to October 13, 2022. The Credit Agreement also includes the option for the Company to increase the size of the Revolving Credit Facility and the Term Loan by up to an additional $300.0 million , in the aggregate, subject to the satisfaction of certain conditions set forth in the Credit Agreement. Term Loans may be made in up to two advances. The first advance of $125.0 million occurred on October 13, 2017 and the second advance of $75.0 million occurred on January 16, 2018. For the Term Loan, the Company is required to make quarterly principal payments of 1.25% of the original term loan ( $2.5 million quarterly) through maturity, with the remaining balance due on October 13, 2022. The Company paid quarterly principal payments of $7.5 million on the term loan during the nine months ended September 28, 2019 . Outstanding borrowings under the Credit Agreement bear interest, at the Company’s option, at either LIBOR, fixed for interest periods of one , two , three or six -month periods, plus 1.00% to 2.00% , or at the bank’s Base Rate, as defined, plus 0.00% to 1.00% , based upon the Company’s Consolidated Leverage Ratio, as defined. The Company is also required to pay commitment fees on unused portions of the credit agreement ranging from 0.15% to 0.25% , based on the Consolidated Leverage Ratio, as defined in the agreement. The credit agreement includes representations, covenants and events of default that are customary for financing transactions of this nature. The effective interest rate on outstanding borrowings under the credit facility was 3.54% at September 28, 2019 . As of September 28, 2019 , the Company had less than $0.1 million outstanding in letters of credit and had available $416.5 million of borrowing capacity under the Revolving Credit Facility based on financial covenants. At September 28, 2019 , the Company was in compliance with all covenants under the Credit Agreement. Senior Notes On December 8, 2016, the Company entered into a Note Purchase Agreement, pursuant to which the Company issued and sold €212 million aggregate principal amount of senior notes in two series. The funding date for the Euro denominated senior notes occurred on December 8, 2016 for €117 million in aggregate amount of 1.14% Senior Notes, Series A, due December 8, 2023 (“Euro Senior Notes, Series A due 2023”), and €95 million in aggregate amount of 1.83% Senior Notes, Series B due December 8, 2028 (“Euro Senior Notes, Series B due 2028”) (together, the “Euro Senior Notes”). Interest on the Euro Senior Notes is payable semiannually on June 8 and December 8, commencing June 8, 2017. On December 8, 2016, the Company entered into a Note Purchase Agreement, pursuant to which the Company issued and sold $125 million aggregate principal amount of senior notes in two series. On February 15, 2017, $25 million in aggregate principal amount of 3.03% Senior Notes, Series A, due February 15, 2022 (“U.S. Senior Notes, Series A due 2022”), and $100 million in aggregate principal amount of 3.74% Senior Notes, Series B, due February 15, 2027 (“U.S. Senior Notes, Series B due 2027”) (together, the “U.S. Senior Notes due 2022 and 2027”) were funded. Interest on the U.S. Senior Notes due 2022 and 2027 is payable semiannually on February 15 and August 15, commencing August 15, 2017. On November 15, 2017, the Company entered into a Note Purchase Agreement pursuant to which the Company issued and sold $175 million in aggregate principal amount of senior notes in two series. On January 16, 2018, $50 million aggregate principal amount of 3.48% Senior Notes, Series A, due February 15, 2025 (“U.S. Senior Notes, Series A due 2025”) and $125 million in aggregate principal amount of 3.78% Senior Notes, Series B, due February 15, 2030 (“U.S. Senior Notes, Series B due 2030”) (together the “U.S. Senior Notes due 2025 and 2030” and with the Euro Senior Notes and the U.S. Senior Notes due 2022 and 2027, the “Senior Notes”) were funded. Interest on the U.S. Senior Notes due 2025 and 2030 is payable semiannually on February 15 and August 15, commencing on August 15, 2018. The Senior Notes have not been registered under the Securities Act, or applicable state securities laws. The Senior Notes are general unsecured senior obligations and rank equal in right of payment with all existing and future unsecured unsubordinated indebtedness of the Company. The Senior Notes are subject to certain customary covenants, including limitations on the Company’s ability, with certain exceptions, to engage in mergers, consolidations, asset sales and transactions with affiliates, to engage in any business that would substantially change the general business of the Company, and to incur liens. In addition, the Company is required to satisfy certain financial covenants and tests relating to, among other matters, interest coverage and leverage. At September 28, 2019 , the Company was in compliance with all covenants under the Senior Notes. The Company may redeem the Senior Notes upon the satisfaction of certain conditions and the payment of a make-whole amount to noteholders, and are required to offer to repurchase the Senior Notes at par following certain events, including a change of control. Interest paid on all Company debt was $6.4 million and $8.1 million for the three months ended September 28, 2019 and September 29, 2018 , respectively, and $17.9 million and $15.8 million for the nine months ended September 28, 2019 and September 29, 2018 , respectively.

Fair Value of Assets and Liabil

Fair Value of Assets and Liabilities	9 Months Ended
	Sep. 28, 2019
Fair Value Disclosures [Abstract]
Fair Value of Assets and Liabilities	Fair Value of Assets and Liabilities For assets and liabilities measured at fair value on a recurring and nonrecurring basis, a three-level hierarchy of measurements based upon observable and unobservable inputs is used to arrive at fair value. Observable inputs are developed based on market data obtained from independent sources, while unobservable inputs reflect the Company’s assumptions about valuation based on the best information available in the circumstances. Depending on the inputs, the Company classifies each fair value measurement as follows: Level 1 —Valuations based on unadjusted quoted prices for identical assets or liabilities in active markets; Level 2 —Valuations based upon quoted prices for similar instruments, prices for identical or similar instruments in markets that are not active, or model-derived valuations, all of whose significant inputs are observable, and Level 3 —Valuations based upon one or more significant unobservable inputs. Following is a description of the valuation methodologies used for instruments measured at fair value and their classification in the valuation hierarchy. Investments in Equity Securities Investments in equity securities listed on a national market or exchange are valued at the last sales price and classified within Level 1 of the valuation hierarchy and recorded in investments and other assets. The Company has certain convertible debt and convertible preferred stock investments that are accounted for under the cost method reflected in other assets in the Condensed Consolidated Balance Sheets. During the nine months ended September 28, 2019 , the Company recorded impairment charges of $2.8 million in Other expense (income), net in the Condensed Consolidated Statements of Net Income to adjust these certain investments to their estimated fair value of $1.2 million . The fair value of these investments are measured on a nonrecurring basis and determined to be Level 3 under the fair value hierarchy. The Company's accounting and finance management determines the valuation policies and procedures for Level 3 fair value measurements and is responsible for the development and determination of unobservable inputs. Mutual Funds The Company has a non-qualified Supplemental Retirement and Savings Plan which provides additional retirement benefits for certain management employees and named executive officers by allowing participants to defer a portion of their annual compensation. The Company maintains accounts for participants through which participants make investment elections. The marketable securities are classified as Level 1 under the fair value hierarchy as they are maintained in mutual funds with readily determinable fair value and recorded in other assets. There were no changes during the quarter ended September 28, 2019 to the Company’s valuation techniques used to measure asset and liability fair values on a recurring basis. As of September 28, 2019 and December 29, 2018 , the Company did not hold any non-financial assets or liabilities that are required to be measured at fair value on a recurring basis. The following table presents assets measured at fair value by classification within the fair value hierarchy as of September 28, 2019 : Fair Value Measurements Using (in thousands) Quoted Prices in Significant Significant Total Investments in equity securities $ 12,648 $ — $ — $ 12,648 Mutual funds 9,717 — — 9,717 The following table presents assets measured at fair value by classification within the fair value hierarchy as of December 29, 2018 : Fair Value Measurements Using (in thousands) Quoted Prices in Significant Significant Total Investments in equity securities $ 10,312 $ — $ — $ 10,312 Mutual funds 9,112 — — 9,112 In addition to the methods and assumptions used for the financial instruments recorded at fair value as discussed above, the following methods and assumptions are used to estimate the fair value of other financial instruments that are not marked to market on a recurring basis. The Company’s other financial instruments include cash and cash equivalents, short-term investments, accounts receivable and its long-term debt. Due to their short-term maturity, the carrying amounts of cash and cash equivalents, short-term investments and accounts receivable approximate their fair values. The Company’s revolving and term loan debt facilities’ fair values approximate book value at September 28, 2019 and December 29, 2018 , as the rates on these borrowings are variable in nature. The carrying value and estimated fair values of the Company’s Euro Senior Notes, Series A and Series B and USD Senior Notes, Series A and Series B, as of September 28, 2019 and December 29, 2018 were as follows: September 28, 2019 December 29, 2018 (in thousands) Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Euro Senior Notes, Series A due 2023 $ 128,002 $ 129,793 $ 133,417 $ 130,888 Euro Senior Notes, Series B due 2028 103,933 109,767 108,330 103,774 USD Senior Notes, Series A due 2022 25,000 25,010 25,000 24,115 USD Senior Notes, Series B due 2027 100,000 103,179 100,000 94,458 USD Senior Notes, Series A due 2025 50,000 50,918 50,000 47,434 USD Senior Notes, Series B due 2030 125,000 128,681 125,000 114,731

Benefit Plans

Benefit Plans	9 Months Ended
	Sep. 28, 2019
Retirement Benefits [Abstract]
Benefit Plans	Benefit Plans The Company has company-sponsored defined benefit pension plans covering employees in the U.K., Germany, the Philippines, China, Japan, Mexico, Italy and France. The amount of the retirement benefits provided under the plans is based on years of service and final average pay. The Company recognizes interest cost, expected return on plan assets, and amortization of prior service, net within Other expense (income), net in the Condensed Consolidated Statements of Net Income. The components of net periodic benefit cost for the three and nine months ended September 28, 2019 and September 29, 2018 were as follows: For the Three Months Ended For the Nine Months Ended (in thousands) September 28, 2019 September 29, 2018 September 28, 2019 September 29, 2018 Components of net periodic benefit cost: Service cost $ 509 $ 533 $ 1,523 $ 1,599 Interest cost 777 501 2,374 1,503 Expected return on plan assets (773 ) (540 ) (2,384 ) (1,620 ) Amortization of prior service 60 74 184 222 Net periodic benefit cost $ 573 $ 568 $ 1,697 $ 1,704 The Company expects to make approximately $2.3 million of cash contributions to its pension plans in 2019.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 28, 2019
Equity [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) Changes in other comprehensive (loss) income by component were as follows: (in thousands) Three Months Ended Three Months Ended Pre-tax Tax Net of Tax Pre-tax Tax Net of Tax Defined benefit pension plan adjustments $ 155 $ 18 $ 137 $ (115 ) $ — $ (115 ) Foreign currency translation adjustments (17,163 ) — (17,163 ) (7,832 ) — (7,832 ) Total change in other comprehensive income (loss) $ (17,008 ) $ 18 $ (17,026 ) $ (7,947 ) $ — $ (7,947 ) (in thousands) Nine Months Ended September 28, 2019 Nine Months Ended September 29, 2018 Pre-tax Tax Net of Tax Pre-tax Tax Net of Tax Defined benefit pension plan adjustments $ 278 $ 29 $ 249 $ 630 $ (18 ) $ 648 Foreign currency translation adjustments (14,933 ) — (14,933 ) (24,816 ) — (24,816 ) Total change in other comprehensive income (loss) $ (14,655 ) $ 29 $ (14,684 ) $ (24,186 ) $ (18 ) $ (24,168 ) The following tables set forth the changes in accumulated other comprehensive (loss) income by component for the nine months ended September 28, 2019 and September 29, 2018 : (in thousands) Pension and postretirement liability and reclassification adjustments Foreign currency translation adjustment Accumulated other comprehensive income (loss) Balance at December 29, 2018 $ (9,959 ) $ (87,965 ) $ (97,924 ) Activity in the period 249 (14,933 ) (14,684 ) Balance at September 28, 2019 $ (9,710 ) $ (102,898 ) $ (112,608 ) (in thousands) Pension and postretirement liability and reclassification adjustments Unrealized gain (loss) on investments Foreign currency translation adjustment Accumulated other comprehensive income (loss) Balance at December 30, 2017 $ (10,836 ) $ 9,795 $ (62,627 ) $ (63,668 ) Cumulative effect adjustment (a) — (9,795 ) — (9,795 ) Activity in the period 648 — (24,816 ) (24,168 ) Balance at September 29, 2018 $ (10,188 ) $ — $ (87,443 ) $ (97,631 ) (a)The Company adopted ASU 2016-01 on December 31, 2017 on a modified retrospective basis, recognizing the cumulative effect as a $9.8 million increase to retained earnings. Amounts reclassified from accumulated other comprehensive (loss) income to earnings for the three and nine months ended September 28, 2019 and September 29, 2018 were as follows: Three Months Ended Nine Months Ended (in thousands) September 28, 2019 September 29, 2018 September 28, 2019 September 29, 2018 Pension and Postemployment plans: Amortization of prior service $ 60 $ 74 $ 184 $ 222 The Company recognizes the amortization of prior service costs in Other (expense) income, net within the Condensed Consolidated Statements of Net Income.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 28, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rate for the three and nine months ended September 28, 2019 was 13.9% and 17.7% respectively, compared to the effective tax rate for the three and nine months ended September 29, 2018 of 21.5% and 20.1% respectively. The effective tax rates for the 2019 periods are lower than the effective tax rates for the 2018 periods primarily due to lower taxes in certain non-US jurisdictions, including the impact of a tax holiday in China which was applicable in the 2019 periods but not in the 2018 periods. The effective tax rates for the 2019 periods were lower than the applicable U.S. statutory tax rate primarily due to income earned in lower tax jurisdictions.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 28, 2019
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share The following table sets forth the computation of basic and diluted earnings per share: Three Months Ended Nine Months Ended (in thousands, except per share amounts) September 28, 2019 September 29, 2018 September 28, 2019 September 29, 2018 Numerator: Net income as reported $ 35,647 $ 53,546 $ 116,428 $ 131,900 Denominator: Weighted average shares outstanding Basic 24,482 25,109 24,646 24,817 Effect of dilutive securities 202 362 248 395 Diluted 24,684 25,471 24,894 25,212 Earnings Per Share: Basic earnings per share $ 1.46 $ 2.13 $ 4.72 $ 5.31 Diluted earnings per share $ 1.44 $ 2.10 $ 4.68 $ 5.23 Potential shares of common stock relating to stock options excluded from the earnings per share calculation because their effect would be anti-dilutive were 205,516 and 38,082 for the three months ended September 28, 2019 and September 29, 2018 , respectively, and 147,090 and 39,446 for the nine months ended September 28, 2019 and September 29, 2018 , respectively. Share Repurchase Program The Company’s Board of Directors authorized the repurchase of up to 1,000,000 shares of the Company’s common stock under a program for the period May 1, 2018 to April 30, 2019 ("2018 program"). On April 26, 2019, the Company's Board of Directors authorized a new program to repurchase up to 1,000,000 shares of the Company's common stock for the period May 1, 2019 to April 30, 2020 ("2019 program"). During the three and nine months ended September 28, 2019 , the Company repurchased 311,786 and 579,916 shares of its common stock totaling $49.5 million and $95.0 million , respectively.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 28, 2019
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions As a result of the Company’s acquisition of IXYS, the Company has equity ownership in various investments that are accounted for under the equity method and recorded in investments in the Condensed Consolidated Balance Sheets. The following is a description of the investments and related party transactions. Powersem GmbH: The Company owns 45% of the outstanding equity of Powersem GmbH (“Powersem”), a module manufacturer based in Germany. For both the three months ended September 28, 2019 and September 29, 2018 , the Company recorded revenues of $0.2 million from sales of products to Powersem for use as components in their products. For the nine months ended September 28, 2019 and September 29, 2018 , the Company recorded revenues of $0.4 million and $0.6 million from sales of products to Powersem for use as components in their products, respectively. During the three months ended September 28, 2019 and September 29, 2018 , the Company purchased $0.8 million and $1.3 million of products from Powersem, respectively. During the nine months ended September 28, 2019 and September 29, 2018 , the Company purchased $2.4 million and $3.4 million of products from Powersem, respectively. As of September 28, 2019 , the accounts receivable balance from Powersem was $0.1 million and the accounts payable balance to Powersem was $0.1 million . As of December 29, 2018 , the trade receivable balance from Powersem was $0.1 million and the accounts payable balance to Powersem was $0.2 million . EB-Tech Co., Ltd.: The Company owns approximately 19% of the outstanding equity of EB Tech Co., Ltd. (“EB Tech”), a company with expertise in radiation technology based in South Korea. During both the three months ended September 28, 2019 and September 29, 2018 , EB Tech rendered processing services for the Company totaling less than $0.1 million . During both the nine months ended September 28, 2019 and September 29, 2018 , EB Tech rendered processing services for the Company totaling approximately $0.3 million . As of September 28, 2019 the Company's accounts payable balance to EB Tech was less than $0.1 million . As of December 29, 2018 , the Company’s accounts payable balance to EB Tech was $0.1 million . Automated Technology (Phil), Inc. : The Company owns approximately 24% of the outstanding common shares of Automated Technology (Phil), Inc. (“ATEC”), a supplier located in the Philippines that provides assembly and test services. During the three months ended September 28, 2019 and September 29, 2018 , ATEC rendered assembly and test services to the Company totaling approximately $1.7 million and $2.5 million , respectively. During the nine months ended September 28, 2019 and September 29, 2018 , ATEC rendered assembly and test services to the Company totaling approximately $5.5 million and $7.7 million , respectively. As of September 28, 2019 the Company's accounts payable balance to ATEC was $0.2 million . As of December 29, 2018 , the Company’s accounts payable balance to ATEC was $0.5 million . Additionally, the Company has certain cost method investments in VTOOL Ltd. and Securepush Ltd. with a total book value of $1.2 million as of September 28, 2019 where one member of the Company’s Board of Directors is currently an investor and a director of VTOOL Ltd. and Securepush Ltd. On March 25, 2019, the Company entered into a definitive agreement to sell the assets and liabilities of Microwave Technology, Inc. (“MWT”) resulting in a loss on disposal of $2.6 million reflected in Other income (expense), net in the Condensed Consolidated Statements of Net Income. The operations of Microwave Technology, Inc. were included in the Electronics segment. One member of the Company’s Board of Directors is the co-owner of a company that agreed to purchase MWT. This transaction closed on April 26, 2019.

Segment Information

Segment Information	9 Months Ended
	Sep. 28, 2019
Segment Reporting [Abstract]
Segment Information	Segment Information The Company and its subsidiaries design, manufacture and sell components and modules for circuit protection, power control and sensing throughout the world. The Company reports its operations by the following segments: Electronics, Automotive, and Industrial. An operating segment is defined as a component of an enterprise that engages in business activities from which it may earn revenues and incur expenses, and about which separate financial information is regularly evaluated by the Chief Operating Decision Maker (“CODM”) in deciding how to allocate resources. The CODM is the Company’s President and Chief Executive Officer (“CEO”). The CODM allocates resources to and assesses the performance of each operating segment using information about its revenue and operating income (loss) before interest and taxes, but does not evaluate the operating segments using discrete balance sheet information. Sales, marketing, and research and development expenses are charged directly into each operating segment. Manufacturing, purchasing, logistics, customer service, finance, information technology, and human resources are shared functions that are allocated back to the three operating segments. The Company does not report inter-segment revenue because the operating segments do not record it. Certain expenses, determined by the CODM to be strategic in nature and not directly related to segments current results, are not allocated but identified as “Other”. Additionally, the Company does not allocate interest and other income, interest expense, or taxes to operating segments. These costs are not allocated to the segments, as management excludes such costs when assessing the performance of the segments. Although the CODM uses operating income (loss) to evaluate the segments, operating costs included in one segment may benefit other segments. Except as discussed above, the accounting policies for segment reporting are the same as for the Company as a whole. • Electronics Segment : Consists of one of the broadest product offerings in the industry, including fuses and fuse accessories, positive temperature coefficient (“PTC”) resettable fuses, polymer electrostatic discharge (“ESD”) suppressors, varistors, reed switch based magnetic sensing, gas discharge tubes; semiconductor and power semiconductor products such as discrete transient voltage suppressor (“TVS”) diodes, TVS diode arrays, protection and switching thyristors, silicon carbide, metal-oxide-semiconductor field-effect transistors (“MOSFETs”) and silicon carbide diodes; and insulated gate bipolar transistors (“IGBT”) technologies. The segment covers a broad range of end markets, including industrial and automotive electronics, electric vehicle infrastructure, data and telecommunications, medical devices, LED lighting, consumer electronics and appliances • Automotive Segment: Consists of a wide range of circuit protection, power control and sensing technologies for global original equipment manufacturers (“OEMs”), Tier-I suppliers and parts distributors in passenger car, heavy duty truck, off-road vehicles, material handling, agricultural, construction and other commercial vehicle industries. Passenger car fuse products include fuses and fuse accessories for internal combustion engine vehicles and hybrid and electric vehicles including blade fuses, battery cable protectors, resettable fuses, high-current fuses, and high-voltage fuses. Commercial vehicle products include fuses, switches, relays, and power distribution modules for the commercial vehicle industry. Automotive sensor products include a wide range of automotive and commercial vehicle products designed to monitor the passenger compartment occupants, safety and environment as well as the vehicle’s powertrain, emissions, speed and suspension. • Industrial Segment: Consists of power fuses, protection relays and controls and other circuit protection products for use in various industrial applications such as oil, gas, mining, alternative energy - solar and wind, electric vehicle infrastructure, construction, HVAC systems, elevator and other industrial equipment. Segment information is summarized as follows: Three Months Ended Nine Months Ended (in thousands) September 28, 2019 September 29, 2018 September 28, 2019 September 29, 2018 Net sales Electronics $ 227,252 $ 296,472 $ 752,199 $ 860,240 Automotive 104,681 114,416 326,814 367,718 Industrial 30,038 28,303 86,337 88,229 Total net sales $ 361,971 $ 439,191 $ 1,165,350 $ 1,316,187 Depreciation and amortization Electronics $ 14,960 $ 15,898 $ 45,031 45,227 Automotive 7,067 5,891 20,848 17,830 Industrial 1,061 1,364 3,177 4,291 Other — 3,105 — 8,712 Total depreciation and amortization $ 23,088 $ 26,258 $ 69,056 $ 76,060 Operating income (loss) Electronics $ 34,567 $ 72,464 $ 127,233 $ 193,739 Automotive 11,437 10,863 34,987 44,965 Industrial 6,822 4,134 16,158 14,123 Other (a) (5,659 ) (11,233 ) (17,904 ) (79,406 ) Total operating income 47,167 76,228 160,474 173,421 Interest expense 5,559 5,775 16,834 16,980 Foreign exchange loss (gain) 4,968 982 5,636 (6,372 ) Other (income) expense, net (4,764 ) 1,259 (3,406 ) (2,362 ) Income before income taxes $ 41,404 $ 68,212 $ 141,410 $ 165,175 (a) Included in “Other” Operating income (loss) for the 2019 third quarter is $3.2 million ( $6.9 million year-to-date) of acquisition related and integration charges primarily related to the IXYS acquisition. In addition, there were $2.5 million ( $11.0 million year-to-date) of restructuring charges primarily related to employee termination costs. See Note 8, Restructuring, Impairment and Other Charges, for further discussion. Included in "Other" Operating income (loss) for the third quarter of 2018 is includes approximately $10.1 million ( $75.6 million year-to-date) of charges related to the IXYS acquisition, which include $36.9 million year-to-date of purchase accounting inventory step-up charges previously recorded during the first and second quarters of 2018, $2.4 million ( $16.1 million year-to-date) in acquisition-related and integration costs primarily related to legal, accounting and other expenses, $3.1 million ( $8.7 million year-to-date) in backlog amortization costs, $4.6 million ( $7.3 million year-to-date) of employee termination costs and other restructuring charges, and $4.5 million year-to-date stock compensation expense recognized immediately upon close for converted IXYS options related to prior service periods and $2.1 million year-to-date change in control expense related to IXYS. In addition, there were $0.4 million ( $1.6 million year-to-date) of employee termination costs, other restructuring, impairment charges of $1.1 million associated with the exit of the Custom business in the second quarter, and $0.7 million ( $1.1 million year-to-date) of acquisition-related expenses for other contemplated acquisitions. The Company’s net sales by country were as follows: Three Months Ended Nine Months Ended (in thousands) September 28, 2019 September 29, 2018 September 28, 2019 September 29, 2018 Net sales United States $ 105,292 $ 125,867 $ 340,811 $ 386,980 China 101,960 117,813 316,553 352,097 Other countries (a) 154,719 195,511 507,986 577,110 Total net sales $ 361,971 $ 439,191 $ 1,165,350 $ 1,316,187 The Company’s long-lived assets by country were as follows: (in thousands) September 28, December 29, Long-lived assets United States $ 56,790 $ 58,691 China 88,386 95,806 Mexico 73,350 70,495 Germany 35,817 36,548 Philippines 37,775 32,459 Other countries (a) 37,674 45,895 Total long-lived assets $ 329,792 $ 339,894 The Company’s additions to long-lived assets by country were as follows: Nine Months Ended (in thousands) September 28, 2019 September 29, 2018 Additions to long-lived assets United States $ 4,972 $ 5,636 China 12,418 19,043 Mexico 12,650 14,089 Germany 4,335 5,917 Philippines 9,546 6,133 Other countries (a) 3,454 5,128 Total additions to long-lived assets $ 47,375 $ 55,946 (a) Each country included in other countries are less than 10% of net sales.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies and Other Information (Policies)	9 Months Ended
	Sep. 28, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company’s accompanying unaudited Condensed Consolidated Financial Statements have been prepared in accordance with U.S. Generally Accepted Accounting Principles (“GAAP”) for interim financial information, the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, certain information and disclosures normally included in the consolidated balance sheets, statements of net income and comprehensive income, statements of cash flows, and statement of stockholders' equity prepared in conformity with U.S. GAAP have been condensed or omitted as permitted by such rules and regulations, although the Company believes that the disclosures made are adequate to make the information not misleading. They have been prepared in accordance with accounting policies described in the Company’s Annual Report on Form 10-K for the fiscal year ended December 29, 2018 which should be read in conjunction with the disclosures therein. In the opinion of management, all adjustments considered necessary for a fair presentation have been included and are of a normal, recurring nature. Operating results for interim periods are not necessarily indicative of annual operating results.
Revenue Recognition	Revenue Recognition On December 31, 2017, the Company adopted new guidance on revenue from contracts with customers using the modified retrospective method. The adoption did not have a significant impact on the Company’s consolidated financial statements. Revenue Disaggregation The following tables disaggregate the Company’s revenue by primary business units for the three and nine months ended September 28, 2019 and September 29, 2018 : Three Months Ended September 28, 2019 Nine Months Ended September 28, 2019 (in thousands) Electronics Segment Automotive Segment Industrial Segment Total Electronics Segment Automotive Segment Industrial Segment Total Electronics – Passive Products and Sensors $ 94,766 $ — $ — $ 94,766 $ 311,624 $ — $ — $ 311,624 Electronics – Semiconductor 132,486 — — 132,486 440,575 — — 440,575 Passenger Car Products — 53,889 — 53,889 — 164,348 — 164,348 Automotive Sensors — 23,877 — 23,877 — 74,616 — 74,616 Commercial Vehicle Products — 26,915 — 26,915 — 87,850 — 87,850 Industrial Products — — 30,038 30,038 — — 86,337 86,337 Total $ 227,252 $ 104,681 $ 30,038 $ 361,971 $ 752,199 $ 326,814 $ 86,337 $ 1,165,350 Three Months Ended September 29, 2018 Nine Months Ended September 29, 2018 (in thousands) Electronics Segment Automotive Segment Industrial Segment Total Electronics Segment Automotive Segment Industrial Segment Total Electronics – Passive Products and Sensors $ 124,174 $ — $ — $ 124,174 $ 366,990 $ — $ — $ 366,990 Electronics – Semiconductor 172,298 — — 172,298 493,250 — — 493,250 Passenger Car Products — 57,761 — 57,761 — 184,922 — 184,922 Automotive Sensors — 27,311 — 27,311 — 89,362 — 89,362 Commercial Vehicle Products — 29,344 — 29,344 — 93,434 — 93,434 Industrial Products — — 28,303 28,303 — — 88,229 88,229 Total $ 296,472 $ 114,416 $ 28,303 $ 439,191 $ 860,240 $ 367,718 $ 88,229 $ 1,316,187 See Note 16, Segment Information for net sales by segment and countries. Revenue Recognition The Company recognizes revenue on product sales in the period in which the Company satisfies its performance obligation and control of the product is transferred to the customer. The Company’s sales arrangements with customers are predominately short term in nature and generally provide for transfer of control at the time of shipment as this is the point at which title and risk of loss of the product transfers to the customer. At the end of each period, for those shipments where title to the products and the risk of loss and rewards of ownership do not transfer until the product has been received by the customer, the Company adjusts revenues and cost of sales for the delay between the time that the products are shipped and when they are received by the customer. The amount of revenue recorded reflects the consideration to which the Company expects to be entitled in exchange for goods and may include adjustments for customer allowance, rebates and price adjustments. The Company’s distribution channels are primarily through direct sales and independent third-party distributors. The Company elected the practical expedient under Accounting Standards Codification ("ASC") 340-40-25-4 to expense commissions when incurred as the amortization period of the commission asset the Company would have otherwise recognized is less than one year. Revenue and Billing The Company generally accepts orders from customers through receipt of purchase orders or electronic data interchange based on written sales agreements and purchasing contracts. Contract pricing and selling agreement terms are based on market factors, costs, and competition. Pricing is often negotiated as an adjustment (premium or discount) from the Company’s published price lists. The customer is invoiced when the Company’s products are shipped to them in accordance with the terms of the sales agreement. As the Company’s standard payment terms are less than one year, the Company elected the practical expedient under ASC 606-10-32-18 to not assess whether a contract has a significant financing component. The Company also elected the practical expedient provided in ASC 606-10-25-18B to treat all product shipping and handling activities as fulfillment activities, and therefore recognize the gross revenue associated with the contract, inclusive of any shipping and handling revenue. This is similar to the Company’s prior practice and therefore the effect of the new guidance is immaterial. Ship and Debit Program Some of the terms of the Company’s sales agreements and normal business conditions provide customers (distributors) the ability to receive price adjustments on products previously shipped and invoiced. This practice is common in the industry and is referred to as a “ship and debit” program. This program allows the distributor to debit the Company for the difference between the distributors’ contracted price and a lower price for specific transactions. Under certain circumstances (usually in a competitive situation or large volume opportunity), a distributor will request authorization for pricing allowances to reduce its price. When the Company approves such a reduction, the distributor is authorized to “debit” its account for the difference between the contracted price and the lower approved price. The Company establishes reserves for this program based on historic activity and actual authorizations for the debit and recognizes these debits as a reduction of revenue. Return to Stock The Company has a return to stock policy whereby certain customers, with prior authorization from Littelfuse management, can return previously purchased goods for full or partial credit. The Company establishes an estimated allowance for these returns based on historic activity. Sales revenue and cost of sales are reduced to anticipate estimated returns. Volume Rebates The Company offers volume based sales incentives to certain customers to encourage greater product sales. If customers achieve their specific quarterly or annual sales targets, they are entitled to rebates. The Company estimates the projected amount of rebates that will be achieved by the customer and recognizes this estimated cost as a reduction to revenue as products are sold.
Recently Adopted and Issued Accounting Standards	Recently Adopted Accounting Standards In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, "Leases" (Topic 842), ("ASC 842"). This ASU requires lessees to recognize, on the balance sheet, assets and liabilities for the rights and obligations created by leases of greater than twelve months. The accounting by lessors will remain largely unchanged. The ASU is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. Adoption requires using a modified retrospective transition with either 1) periods prior to the adoption date being recast or 2) a cumulative-effect adjustment recognized to the opening balance of retained earnings on the adoption date with prior periods not recast. The Company adopted the standard on December 30, 2018 using alternative modified retrospective transition method provided in ASU No. 2018-11, "Leases (Topic 842): Target Improvements." Under this method, the Company recorded a cumulative-effect adjustment as of December 30, 2018 and did not record any retrospective adjustments to comparative periods to reflect the adoption of ASC 842. The new standard provides a number of optional practical expedients in transition. The Company has elected the ‘package of practical expedients’ which permits us not to reassess under the new standard our prior conclusions about lease identification, lease classification and initial direct costs. The Company has not elected the use-of-hindsight. Adoption of ASC 842 resulted in the recognition of operating lease right-of-use assets ("ROU") net of deferred rent of $26.1 million and lease liabilities of $29.4 million , as of December 30, 2018 for operating leases on its Condensed Consolidated Balance Sheets, with no impact to its Condensed Consolidated Statements of Net Income and no impact on Condensed Consolidated Statements of Cash Flow. See Note 6, Lease Commitments, for further discussion. In February 2018, the FASB issued ASU No. 2018-02 “Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income,” which permits the reclassification of tax effects stranded in accumulated other comprehensive income to retained earnings as a result of the Tax Act. The standard also requires entities to disclose whether or not they elected to reclassify the tax effects related to the Tax Act as well as their policy for releasing income tax effects from accumulated other comprehensive income. The standard allows the option of applying either a retrospective adoption, meaning the standard is applied to all periods in which the effect of the Tax Act is recognized, or applying the amendments in the period of adoption, meaning an adjustment is made to shareholder’s equity as of the beginning of the reporting period. The Company adopted the new standard on December 30, 2018. The adoption of this guidance did not have a material effect on our Condensed Consolidated Financial Statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies and Other Information (Tables)	9 Months Ended
	Sep. 28, 2019
Accounting Policies [Abstract]
Revenue Disaggregation	The following tables disaggregate the Company’s revenue by primary business units for the three and nine months ended September 28, 2019 and September 29, 2018 : Three Months Ended September 28, 2019 Nine Months Ended September 28, 2019 (in thousands) Electronics Segment Automotive Segment Industrial Segment Total Electronics Segment Automotive Segment Industrial Segment Total Electronics – Passive Products and Sensors $ 94,766 $ — $ — $ 94,766 $ 311,624 $ — $ — $ 311,624 Electronics – Semiconductor 132,486 — — 132,486 440,575 — — 440,575 Passenger Car Products — 53,889 — 53,889 — 164,348 — 164,348 Automotive Sensors — 23,877 — 23,877 — 74,616 — 74,616 Commercial Vehicle Products — 26,915 — 26,915 — 87,850 — 87,850 Industrial Products — — 30,038 30,038 — — 86,337 86,337 Total $ 227,252 $ 104,681 $ 30,038 $ 361,971 $ 752,199 $ 326,814 $ 86,337 $ 1,165,350 Three Months Ended September 29, 2018 Nine Months Ended September 29, 2018 (in thousands) Electronics Segment Automotive Segment Industrial Segment Total Electronics Segment Automotive Segment Industrial Segment Total Electronics – Passive Products and Sensors $ 124,174 $ — $ — $ 124,174 $ 366,990 $ — $ — $ 366,990 Electronics – Semiconductor 172,298 — — 172,298 493,250 — — 493,250 Passenger Car Products — 57,761 — 57,761 — 184,922 — 184,922 Automotive Sensors — 27,311 — 27,311 — 89,362 — 89,362 Commercial Vehicle Products — 29,344 — 29,344 — 93,434 — 93,434 Industrial Products — — 28,303 28,303 — — 88,229 88,229 Total $ 296,472 $ 114,416 $ 28,303 $ 439,191 $ 860,240 $ 367,718 $ 88,229 $ 1,316,187

Acquisitions (Tables)

Acquisitions (Tables)	9 Months Ended
	Sep. 28, 2019
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table summarizes the purchase price allocation of the fair value of assets acquired and liabilities assumed in the IXYS acquisition: (in thousands) Purchase Price Allocation Total purchase consideration: Cash, net of cash acquired $ 302,865 Cash settled stock options 3,622 Littelfuse stock 434,192 Converted stock options 38,109 Total purchase consideration $ 778,788 Allocation of consideration to assets acquired and liabilities assumed: Current assets, net $ 155,930 Property, plant, and equipment 77,442 Intangible assets 212,720 Goodwill 382,360 Other non-current assets 28,706 Other non-current liabilities (78,370 ) $ 778,788
Business Acquisition, Pro Forma Information	The following table summarizes, on a pro forma basis, the combined results of operations of the Company and IXYS as though the acquisition had occurred as of January 1, 2017. The pro forma amounts presented are not necessarily indicative of either the actual consolidated results had the IXYS acquisition occurred as of January 1, 2017 or of future consolidated operating results. Three Months Ended Nine Months Ended (in thousands, except per share amounts) September 29, 2018 September 29, 2018 Net sales $ 439,191 $ 1,332,900 Income before income taxes 71,737 228,503 Net income 56,060 179,264 Net income per share — basic 2.23 7.17 Net income per share — diluted 2.18 7.16
Business Acquisition, Pro Forma Information, Nonrecurring Adjustments	Pro forma results presented above primarily reflect the following adjustments: Three Months Ended Nine Months Ended (in thousands) September 29, 2018 September 29, 2018 Amortization(a) $ 3,104 $ 8,289 Transaction costs(b) — 9,976 Amortization of inventory step-up(c) — 36,927 Stock compensation(d) 421 5,110 Income tax impact of above items (1,011 ) (14,290 ) (a) The amortization adjustment for the three and nine months ended September 29, 2018 primarily reflects the reduction of amortization expense in the period related to the Order backlog intangible asset. The Order backlog has a useful life of twelve months and was fully amortized in the fiscal 2017 pro forma results. (b) The transaction cost adjustments reflect the reversal of certain bank and attorney fees from the nine months ended September 29, 2018 and recognition of those fees during the nine months ended September 30, 2017. (c) The amortization of inventory step-up adjustment reflects the reversal of the amount recognized during the three and nine months ended September 29, 2018 and recognition of those costs during the three and nine months ended September 30, 2017. The inventory step-up was amortized over five months as the inventory was sold. (d) The stock compensation adjustment reflects the reversal of the portion of stock compensation for IXYS stock options that were converted to Littelfuse stock options and expensed immediately during the nine months ended September 29, 2018 .

Inventories (Tables)

Inventories (Tables)	9 Months Ended
	Sep. 28, 2019
Inventory Disclosure [Abstract]
Schedule of Inventory	The components of inventories at September 28, 2019 and December 29, 2018 are as follows: (in thousands) September 28, 2019 December 29, 2018 Raw materials $ 71,327 $ 69,883 Work in process 78,022 88,505 Finished goods 90,710 99,840 Total $ 240,059 $ 258,228

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	9 Months Ended
	Sep. 28, 2019
Property, Plant and Equipment [Abstract]
Components of net property, plant, and equipment	The components of net property, plant, and equipment at September 28, 2019 and December 29, 2018 are as follows: (in thousands) September 28, 2019 December 29, 2018 Land $ 24,699 $ 25,630 Building 106,062 114,636 Equipment 605,965 583,043 Accumulated depreciation and amortization (406,934 ) (383,415 ) Total $ 329,792 $ 339,894

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	9 Months Ended
	Sep. 28, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The amounts for goodwill and changes in the carrying value by segment for the nine months ended September 28, 2019 are as follows: (in thousands) Electronics Automotive Industrial Total As of December 29, 2018 $ 656,039 $ 132,332 $ 38,344 $ 826,715 Currency translation (10,627 ) (2,530 ) 95 (13,062 ) As of September 28, 2019 $ 645,412 $ 129,802 $ 38,439 $ 813,653
Schedule of Finite-Lived Intangible Assets	The components of other intangible assets at September 28, 2019 are as follows: (in thousands) Gross Carrying Value Accumulated Amortization Net Book Value Patents, licenses and software $ 136,565 $ 76,797 $ 59,768 Distribution network 43,638 36,014 7,624 Customer relationships, trademarks, and tradenames 372,627 113,602 259,025 Total $ 552,830 $ 226,413 $ 326,417
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Estimated annual amortization expense related to intangible assets with definite lives as of September 28, 2019 is as follows: (in thousands) Amount 2019 $ 41,376 2020 39,206 2021 37,606 2022 36,532 2023 32,150 2024 and thereafter 169,616 Total $ 356,486

Lease Commitments (Tables)

Lease Commitments (Tables)	9 Months Ended
	Sep. 28, 2019
Leases [Abstract]
Supplemental balance sheet information related to leases	The following table presents the classification of ROU assets and lease liabilities as of September 28, 2019 : Leases (in thousands) Condensed Consolidated Balance Sheet Classification September 28, 2019 Assets Operating ROU assets Right of use lease assets, net $ 21,598 Liabilities Current operating lease liabilities Accrued liabilities $ 6,926 Non-current operating lease liabilities Non-current operating lease liabilities 17,237 Total lease liabilities $ 24,163
Components of lease expense and supplemental cash flow information	Other Information (in thousands) Nine Months Ended Cash paid for amounts included in the measurement of lease liabilities Operating cash flow payments for operating leases $ (6,762 ) Leased assets obtained in exchange for operating lease liabilities 2,051 The following table represents the lease costs for the three and nine months ended ended September 28, 2019 : Leases cost (in thousands) Condensed Consolidated Statements of Net Income Classification Three Months Ended September 28, 2019 Nine Months Ended Short-term lease expenses Cost of sales, SG&A expenses $ 86 $ 387 Variable lease expenses Cost of sales, SG&A expenses 239 621 Operating lease rent expenses Cost of sales, SG&A expenses 2,131 6,539 Total operating lease costs Cost of sales, SG&A expenses $ 2,456 $ 7,547
Maturities of lease liabilities	Maturity of Lease Liabilities as of September 28, 2019 (in thousands) Operating leases 2019 (excluding the nine months ended September 28, 2019) $ 2,155 2020 7,571 2021 5,878 2022 4,873 2023 3,252 2024 and thereafter 3,253 Total lease payments $ 26,982 Present value of lease liabilities $ 24,163
Operating lease term and discount rate	Operating Lease Term and Discount Rate September 28, 2019 Weighted-average remaining lease term (years) 4.19 Weighted-average discount rate 5.18 %

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	9 Months Ended
	Sep. 28, 2019
Payables and Accruals [Abstract]
Components of accrued liabilities	The components of accrued liabilities at September 28, 2019 and December 29, 2018 are as follows: (in thousands) September 28, 2019 December 29, 2018 Employee-related liabilities $ 42,076 $ 60,640 Other non-income taxes 32,453 21,523 Operating lease liability 6,926 — Professional services 4,117 6,169 Interest 3,239 5,137 Accrued share repurchases — 4,349 Restructuring liability 2,302 3,887 Other 23,436 36,700 Total $ 114,549 $ 138,405

Restructuring, Impairment and_2

Restructuring, Impairment and Other Charges (Tables)	9 Months Ended
	Sep. 28, 2019
Restructuring and Related Activities [Abstract]
Restructuring, impairment and other charges	The Company recorded restructuring, impairment and other charges for the three and nine months ended September 28, 2019 and September 29, 2018 as follows: Three months ended September 28, 2019 Nine months ended September 28, 2019 (in thousands) Electronics Automotive Industrial Total Electronics Automotive Industrial Total Employee terminations $ 655 $ 109 $ 49 $ 813 $ 4,153 $ 3,955 $ 770 $ 8,878 Other restructuring charges 128 1,150 124 1,402 141 1,240 374 1,755 Total restructuring charges 783 1,259 173 2,215 4,294 5,195 1,144 10,633 Impairment — 322 — 322 — 322 — 322 Total $ 783 $ 1,581 $ 173 $ 2,537 $ 4,294 $ 5,517 $ 1,144 $ 10,955 Three months ended September 29, 2018 Nine months ended September 29, 2018 (in thousands) Electronics Automotive Industrial Total Electronics Automotive Industrial Total Employee terminations $ 4,614 $ 202 $ — $ 4,816 $ 7,693 $ 301 $ 65 $ 8,059 Other restructuring charges — 166 — 166 670 166 — 836 Total restructuring charges 4,614 368 — 4,982 8,363 467 65 8,895 Impairment — — — — — 88 1,037 1,125 Total $ 4,614 $ 368 $ — $ 4,982 $ 8,363 $ 555 $ 1,102 $ 10,020

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 28, 2019
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	The carrying amounts of debt at September 28, 2019 and December 29, 2018 are as follows: (in thousands) September 28, December 29, Term Loan $ 147,500 $ 155,000 Euro Senior Notes, Series A due 2023 128,002 133,417 Euro Senior Notes, Series B due 2028 103,932 108,330 U.S. Senior Notes, Series A due 2022 25,000 25,000 U.S. Senior Notes, Series B due 2027 100,000 100,000 U.S. Senior Notes, Series A due 2025 50,000 50,000 U.S. Senior Notes, Series B due 2030 125,000 125,000 Other 2,619 2,619 Unamortized debt issuance costs (3,893 ) (4,636 ) Total debt 678,160 694,730 Less: Current maturities (10,000 ) (10,000 ) Total long-term debt $ 668,160 $ 684,730

Fair Value of Assets and Liab_2

Fair Value of Assets and Liabilities (Tables)	9 Months Ended
	Sep. 28, 2019
Fair Value Disclosures [Abstract]
Fair Value, Assets Measured on Recurring Basis	The following table presents assets measured at fair value by classification within the fair value hierarchy as of September 28, 2019 : Fair Value Measurements Using (in thousands) Quoted Prices in Significant Significant Total Investments in equity securities $ 12,648 $ — $ — $ 12,648 Mutual funds 9,717 — — 9,717 The following table presents assets measured at fair value by classification within the fair value hierarchy as of December 29, 2018 : Fair Value Measurements Using (in thousands) Quoted Prices in Significant Significant Total Investments in equity securities $ 10,312 $ — $ — $ 10,312 Mutual funds 9,112 — — 9,112
Fair Value, by Balance Sheet Grouping	The carrying value and estimated fair values of the Company’s Euro Senior Notes, Series A and Series B and USD Senior Notes, Series A and Series B, as of September 28, 2019 and December 29, 2018 were as follows: September 28, 2019 December 29, 2018 (in thousands) Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Euro Senior Notes, Series A due 2023 $ 128,002 $ 129,793 $ 133,417 $ 130,888 Euro Senior Notes, Series B due 2028 103,933 109,767 108,330 103,774 USD Senior Notes, Series A due 2022 25,000 25,010 25,000 24,115 USD Senior Notes, Series B due 2027 100,000 103,179 100,000 94,458 USD Senior Notes, Series A due 2025 50,000 50,918 50,000 47,434 USD Senior Notes, Series B due 2030 125,000 128,681 125,000 114,731

Benefit Plans (Tables)

Benefit Plans (Tables)	9 Months Ended
	Sep. 28, 2019
Retirement Benefits [Abstract]
Schedule of Net Benefit Costs	The components of net periodic benefit cost for the three and nine months ended September 28, 2019 and September 29, 2018 were as follows: For the Three Months Ended For the Nine Months Ended (in thousands) September 28, 2019 September 29, 2018 September 28, 2019 September 29, 2018 Components of net periodic benefit cost: Service cost $ 509 $ 533 $ 1,523 $ 1,599 Interest cost 777 501 2,374 1,503 Expected return on plan assets (773 ) (540 ) (2,384 ) (1,620 ) Amortization of prior service 60 74 184 222 Net periodic benefit cost $ 573 $ 568 $ 1,697 $ 1,704

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 28, 2019
Equity [Abstract]
Schedule of Components of Comprehensive Income (Loss)	Changes in other comprehensive (loss) income by component were as follows: (in thousands) Three Months Ended Three Months Ended Pre-tax Tax Net of Tax Pre-tax Tax Net of Tax Defined benefit pension plan adjustments $ 155 $ 18 $ 137 $ (115 ) $ — $ (115 ) Foreign currency translation adjustments (17,163 ) — (17,163 ) (7,832 ) — (7,832 ) Total change in other comprehensive income (loss) $ (17,008 ) $ 18 $ (17,026 ) $ (7,947 ) $ — $ (7,947 ) (in thousands) Nine Months Ended September 28, 2019 Nine Months Ended September 29, 2018 Pre-tax Tax Net of Tax Pre-tax Tax Net of Tax Defined benefit pension plan adjustments $ 278 $ 29 $ 249 $ 630 $ (18 ) $ 648 Foreign currency translation adjustments (14,933 ) — (14,933 ) (24,816 ) — (24,816 ) Total change in other comprehensive income (loss) $ (14,655 ) $ 29 $ (14,684 ) $ (24,186 ) $ (18 ) $ (24,168 )
Schedule of Accumulated Other Comprehensive Income (Loss)	The following tables set forth the changes in accumulated other comprehensive (loss) income by component for the nine months ended September 28, 2019 and September 29, 2018 : (in thousands) Pension and postretirement liability and reclassification adjustments Foreign currency translation adjustment Accumulated other comprehensive income (loss) Balance at December 29, 2018 $ (9,959 ) $ (87,965 ) $ (97,924 ) Activity in the period 249 (14,933 ) (14,684 ) Balance at September 28, 2019 $ (9,710 ) $ (102,898 ) $ (112,608 ) (in thousands) Pension and postretirement liability and reclassification adjustments Unrealized gain (loss) on investments Foreign currency translation adjustment Accumulated other comprehensive income (loss) Balance at December 30, 2017 $ (10,836 ) $ 9,795 $ (62,627 ) $ (63,668 ) Cumulative effect adjustment (a) — (9,795 ) — (9,795 ) Activity in the period 648 — (24,816 ) (24,168 ) Balance at September 29, 2018 $ (10,188 ) $ — $ (87,443 ) $ (97,631 ) (a)The Company adopted ASU 2016-01 on December 31, 2017 on a modified retrospective basis, recognizing the cumulative effect as a $9.8 million increase to retained earnings.
Reclassification out of Accumulated Other Comprehensive Income	Amounts reclassified from accumulated other comprehensive (loss) income to earnings for the three and nine months ended September 28, 2019 and September 29, 2018 were as follows: Three Months Ended Nine Months Ended (in thousands) September 28, 2019 September 29, 2018 September 28, 2019 September 29, 2018 Pension and Postemployment plans: Amortization of prior service $ 60 $ 74 $ 184 $ 222

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 28, 2019
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the computation of basic and diluted earnings per share: Three Months Ended Nine Months Ended (in thousands, except per share amounts) September 28, 2019 September 29, 2018 September 28, 2019 September 29, 2018 Numerator: Net income as reported $ 35,647 $ 53,546 $ 116,428 $ 131,900 Denominator: Weighted average shares outstanding Basic 24,482 25,109 24,646 24,817 Effect of dilutive securities 202 362 248 395 Diluted 24,684 25,471 24,894 25,212 Earnings Per Share: Basic earnings per share $ 1.46 $ 2.13 $ 4.72 $ 5.31 Diluted earnings per share $ 1.44 $ 2.10 $ 4.68 $ 5.23

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 28, 2019
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Segment information is summarized as follows: Three Months Ended Nine Months Ended (in thousands) September 28, 2019 September 29, 2018 September 28, 2019 September 29, 2018 Net sales Electronics $ 227,252 $ 296,472 $ 752,199 $ 860,240 Automotive 104,681 114,416 326,814 367,718 Industrial 30,038 28,303 86,337 88,229 Total net sales $ 361,971 $ 439,191 $ 1,165,350 $ 1,316,187 Depreciation and amortization Electronics $ 14,960 $ 15,898 $ 45,031 45,227 Automotive 7,067 5,891 20,848 17,830 Industrial 1,061 1,364 3,177 4,291 Other — 3,105 — 8,712 Total depreciation and amortization $ 23,088 $ 26,258 $ 69,056 $ 76,060 Operating income (loss) Electronics $ 34,567 $ 72,464 $ 127,233 $ 193,739 Automotive 11,437 10,863 34,987 44,965 Industrial 6,822 4,134 16,158 14,123 Other (a) (5,659 ) (11,233 ) (17,904 ) (79,406 ) Total operating income 47,167 76,228 160,474 173,421 Interest expense 5,559 5,775 16,834 16,980 Foreign exchange loss (gain) 4,968 982 5,636 (6,372 ) Other (income) expense, net (4,764 ) 1,259 (3,406 ) (2,362 ) Income before income taxes $ 41,404 $ 68,212 $ 141,410 $ 165,175 (a) Included in “Other” Operating income (loss) for the 2019 third quarter is $3.2 million ( $6.9 million year-to-date) of acquisition related and integration charges primarily related to the IXYS acquisition. In addition, there were $2.5 million ( $11.0 million year-to-date) of restructuring charges primarily related to employee termination costs. See Note 8, Restructuring, Impairment and Other Charges, for further discussion.
Schedule of Disclosure on Geographic Areas, Long-Lived Assets in Individual Foreign Countries by Country	The Company’s net sales by country were as follows: Three Months Ended Nine Months Ended (in thousands) September 28, 2019 September 29, 2018 September 28, 2019 September 29, 2018 Net sales United States $ 105,292 $ 125,867 $ 340,811 $ 386,980 China 101,960 117,813 316,553 352,097 Other countries (a) 154,719 195,511 507,986 577,110 Total net sales $ 361,971 $ 439,191 $ 1,165,350 $ 1,316,187 The Company’s long-lived assets by country were as follows: (in thousands) September 28, December 29, Long-lived assets United States $ 56,790 $ 58,691 China 88,386 95,806 Mexico 73,350 70,495 Germany 35,817 36,548 Philippines 37,775 32,459 Other countries (a) 37,674 45,895 Total long-lived assets $ 329,792 $ 339,894 The Company’s additions to long-lived assets by country were as follows: Nine Months Ended (in thousands) September 28, 2019 September 29, 2018 Additions to long-lived assets United States $ 4,972 $ 5,636 China 12,418 19,043 Mexico 12,650 14,089 Germany 4,335 5,917 Philippines 9,546 6,133 Other countries (a) 3,454 5,128 Total additions to long-lived assets $ 47,375 $ 55,946 (a) Each country included in other countries are less than 10% of net sales.

Summary of Significant Accoun_4

Summary of Significant Accounting Policies and Other Information (Details Textual) - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 30, 2018
Accounting Policies [Abstract]
Right of use lease assets, net	$ 21,598	$ 26,100
Non-current operating lease liabilities	$ 17,237	$ 29,400

Summary of Significant Accoun_5

Summary of Significant Accounting Policies and Other Information - Revenue Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Disaggregation of Revenue [Line Items]
Net sales	$ 361,971	$ 439,191	$ 1,165,350	$ 1,316,187
Electronics – Passive Products and Sensors
Disaggregation of Revenue [Line Items]
Net sales	94,766	124,174	311,624	366,990
Electronics – Semiconductor
Disaggregation of Revenue [Line Items]
Net sales	132,486	172,298	440,575	493,250
Passenger Car Products
Disaggregation of Revenue [Line Items]
Net sales	53,889	57,761	164,348	184,922
Automotive Sensors
Disaggregation of Revenue [Line Items]
Net sales	23,877	27,311	74,616	89,362
Commercial Vehicle Products
Disaggregation of Revenue [Line Items]
Net sales	26,915	29,344	87,850	93,434
Industrial Products
Disaggregation of Revenue [Line Items]
Net sales	30,038	28,303	86,337	88,229
Electronics Segment
Disaggregation of Revenue [Line Items]
Net sales	227,252	296,472	752,199	860,240
Electronics Segment | Electronics – Passive Products and Sensors
Disaggregation of Revenue [Line Items]
Net sales	94,766	124,174	311,624	366,990
Electronics Segment | Electronics – Semiconductor
Disaggregation of Revenue [Line Items]
Net sales	132,486	172,298	440,575	493,250
Electronics Segment | Passenger Car Products
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Electronics Segment | Automotive Sensors
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Electronics Segment | Commercial Vehicle Products
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Electronics Segment | Industrial Products
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Automotive Segment
Disaggregation of Revenue [Line Items]
Net sales	104,681	114,416	326,814	367,718
Automotive Segment | Electronics – Passive Products and Sensors
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Automotive Segment | Electronics – Semiconductor
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Automotive Segment | Passenger Car Products
Disaggregation of Revenue [Line Items]
Net sales	53,889	57,761	164,348	184,922
Automotive Segment | Automotive Sensors
Disaggregation of Revenue [Line Items]
Net sales	23,877	27,311	74,616	89,362
Automotive Segment | Commercial Vehicle Products
Disaggregation of Revenue [Line Items]
Net sales	26,915	29,344	87,850	93,434
Automotive Segment | Industrial Products
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Industrial Segment
Disaggregation of Revenue [Line Items]
Net sales	30,038	28,303	86,337	88,229
Industrial Segment | Electronics – Passive Products and Sensors
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Industrial Segment | Electronics – Semiconductor
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Industrial Segment | Passenger Car Products
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Industrial Segment | Automotive Sensors
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Industrial Segment | Commercial Vehicle Products
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Industrial Segment | Industrial Products
Disaggregation of Revenue [Line Items]
Net sales	$ 30,038	$ 28,303	$ 86,337	$ 88,229

Acquisitions - Narrative (Detai

Acquisitions - Narrative (Details) $ / shares in Units, $ in Thousands	Jan. 17, 2018USD ($)customer$ / shares	Sep. 29, 2018USD ($)	Sep. 28, 2019$ / shares	Sep. 29, 2018USD ($)	Dec. 29, 2018$ / shares
Business Acquisition [Line Items]
Common stock, par value (in dollars per share) | $ / shares			$ 0.01		$ 0.01
Inventory amortization period			5 months
IXYS Corporation
Business Acquisition [Line Items]
Number of customers | customer	3,500
Common stock, par value (in dollars per share) | $ / shares	$ 0.01
Share price (in dollars per share) | $ / shares	$ 23
Share exchange ratio	0.1265
Share price (in dollars per share) | $ / shares	$ 207.5
Consideration excluding value of stock options converted	$ 814,800
Cash	380,600
Littelfuse stock	434,192
Value of options converted	41,700
Consideration transferred	856,500
Receivables	$ 49,100
Net sales		$ 99,700		$ 286,200
Income (loss) before income taxes		(6,200)		25,500
Allocated share based compensation				4,500
Acquisition related costs				11,000
Other | Operating Income (Loss)
Business Acquisition [Line Items]
Inventory adjustment				36,900
Acquisition related costs		10,100		75,600
Employee Stock Option | IXYS Corporation
Business Acquisition [Line Items]
Allocated share based compensation		$ 4,300		11,800
Employee Stock Option | IXYS Corporation | Selling, General and Administrative Expenses
Business Acquisition [Line Items]
Allocated share based compensation				$ 4,500

Acquisitions - Preliminary Pric

Acquisitions - Preliminary Price Allocation (Details) - USD ($) $ in Thousands	Jan. 17, 2018	Sep. 28, 2019	Sep. 29, 2018	Dec. 29, 2018
Total purchase consideration:
Cash, net of cash acquired		$ 775	$ 313,475
Allocation of consideration to assets acquired and liabilities assumed:
Goodwill		$ 813,653		$ 826,715
IXYS Corporation
Total purchase consideration:
Cash, net of cash acquired	$ 302,865
Cash settled stock options	3,622
Littelfuse stock	434,192
Converted stock options	38,109
Total purchase consideration	778,788
Allocation of consideration to assets acquired and liabilities assumed:
Current assets, net	155,930
Property, plant, and equipment	77,442
Intangible assets	212,720
Goodwill	382,360
Other non-current assets	28,706
Other non-current liabilities	(78,370)
Assets acquired and liabilities assumed	$ 778,788

Acquisitions - Business Acquisi

Acquisitions - Business Acquisition Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 29, 2018	Sep. 29, 2018
Business Combinations [Abstract]
Net sales	$ 439,191	$ 1,332,900
Income before income taxes	71,737	228,503
Net income	$ 56,060	$ 179,264
Net income per share — basic (in dollars per share)	$ 2.23	$ 7.17
Net income per share — diluted (in dollars per share)	$ 2.18	$ 7.16

Acquisitions - Pro Forma Inform

Acquisitions - Pro Forma Information Adjustments (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 29, 2018	Sep. 29, 2018
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income	$ 56,060	$ 179,264
Amortization
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income	3,104	8,289
Transaction costs
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income	0	9,976
Amortization of inventory step-up
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income	0	36,927
Stock compensation
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income	421	5,110
Income tax impact of above items
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income	$ (1,011)	$ (14,290)

Inventories - Components of Inv

Inventories - Components of Inventories (Details) - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 29, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 71,327	$ 69,883
Work in process	78,022	88,505
Finished goods	90,710	99,840
Total	$ 240,059	$ 258,228

Property, Plant, and Equipmen_2

Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018	Dec. 29, 2018
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	$ (406,934)		$ (406,934)		$ (383,415)
Net property, plant, and equipment	329,792		329,792		339,894
Depreciation	13,300	$ 13,100	38,988	$ 37,559
Land
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	24,699		24,699		25,630
Building
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	106,062		106,062		114,636
Equipment
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	$ 605,965		$ 605,965		$ 583,043

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Amounts for Goodwill and Changes in Carrying Value by Operating Segment (Details) $ in Thousands	9 Months Ended
	Sep. 28, 2019USD ($)
Goodwill [Roll Forward]
Balance	$ 826,715
Currency translation	(13,062)
Balance	813,653
Electronics
Goodwill [Roll Forward]
Balance	656,039
Currency translation	(10,627)
Balance	645,412
Automotive
Goodwill [Roll Forward]
Balance	132,332
Currency translation	(2,530)
Balance	129,802
Industrial
Goodwill [Roll Forward]
Balance	38,344
Currency translation	95
Balance	$ 38,439

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of intangibles	$ 9,827	$ 13,130	$ 30,068	$ 38,501

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Details of Other Intangible Assets and Related Future Amortization Expense (Details) $ in Thousands	Sep. 28, 2019USD ($)
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 552,830
Accumulated Amortization	226,413
Net Book Value	326,417
Patents, licenses and software
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	136,565
Accumulated Amortization	76,797
Net Book Value	59,768
Distribution network
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	43,638
Accumulated Amortization	36,014
Net Book Value	7,624
Customer relationships, trademarks, and tradenames
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	372,627
Accumulated Amortization	113,602
Net Book Value	$ 259,025

Goodwill and Other Intangible_6

Goodwill and Other Intangible Assets - Estimated Amortization Expense Related to Intangible Assets with Definite Lives (Details) $ in Thousands	Sep. 28, 2019USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2019	$ 41,376
2020	39,206
2021	37,606
2022	36,532
2023	32,150
2024 and thereafter	169,616
Total	$ 356,486

Lease Commitments - Balance She

Lease Commitments - Balance Sheet, Operating Lease Term and Discount Rate (Details) - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 30, 2018	Dec. 29, 2018
Assets
Operating ROU assets	$ 21,598	$ 26,100
Liabilities
Current operating lease liabilities	6,926		$ 0
Non-current operating lease liabilities	17,237	$ 29,400
Total lease liabilities	$ 24,163
Weighted-average remaining lease term (years)	4 years 2 months 8 days
Weighted-average discount rate	5.18%

Lease Commitments - Lease Cost

Lease Commitments - Lease Cost (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 28, 2019	Sep. 28, 2019
Leases [Abstract]
Short-term lease expenses	$ 86	$ 387
Variable lease expenses	239	621
Operating lease rent expenses	2,131	6,539
Total operating lease costs	$ 2,456	$ 7,547

Lease Commitments - Maturities

Lease Commitments - Maturities of Lease Liabilities (Details) $ in Thousands	Sep. 28, 2019USD ($)
Operating Leases
2019 (excluding the nine months ended September 28, 2019)	$ 2,155
2020	7,571
2021	5,878
2022	4,873
2023	3,252
2024 and thereafter	3,253
Total lease payments	26,982
Present value of lease liabilities	$ 24,163

Lease Commitments - Supplementa

Lease Commitments - Supplemental Cash Flow Information (Details) $ in Thousands	9 Months Ended
	Sep. 28, 2019USD ($)
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flow payments for operating leases	$ (6,762)
Leased assets obtained in exchange for operating lease liabilities	$ 2,051

Accrued Liabilities (Details)

Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 29, 2018
Payables and Accruals [Abstract]
Employee-related liabilities	$ 42,076	$ 60,640
Other non-income taxes	32,453	21,523
Operating lease liability	6,926	0
Professional services	4,117	6,169
Interest	3,239	5,137
Accrued share repurchases	0	4,349
Restructuring liability	2,302	3,887
Other	23,436	36,700
Total	$ 114,549	$ 138,405

Restructuring, Impairment and_3

Restructuring, Impairment and Other Charges (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Apr. 30, 2019	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018	Dec. 29, 2018
Restructuring Cost and Reserve [Line Items]
Total restructuring charges		$ 2,215	$ 4,982	$ 10,633	$ 8,895
Impairment charges		322	0	322	1,125
Restructuring costs		2,537	4,982	10,955	10,020
Restructuring reserves		2,300		2,300		$ 3,900
Employee terminations
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 1,700	813	4,816	8,878	8,059
Other restructuring charges
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 1,100	1,402	166	1,755	836
Electronics
Restructuring Cost and Reserve [Line Items]
Total restructuring charges		783	4,614	4,294	8,363
Impairment charges		0	0	0	0
Restructuring costs		783	4,614	4,294	8,363
Electronics | Employee terminations
Restructuring Cost and Reserve [Line Items]
Total restructuring charges		655	4,614	4,153	7,693
Electronics | Other restructuring charges
Restructuring Cost and Reserve [Line Items]
Total restructuring charges		128	0	141	670
Automotive
Restructuring Cost and Reserve [Line Items]
Total restructuring charges		1,259	368	5,195	467
Impairment charges		322	0	322	88
Restructuring costs		1,581	368	5,517	555
Automotive | Employee terminations
Restructuring Cost and Reserve [Line Items]
Total restructuring charges		109	202	3,955	301
Automotive | Other restructuring charges
Restructuring Cost and Reserve [Line Items]
Total restructuring charges		1,150	166	1,240	166
Industrial
Restructuring Cost and Reserve [Line Items]
Total restructuring charges		173	0	1,144	65
Impairment charges		0	0	0	1,037
Restructuring costs		173	0	1,144	1,102
Industrial | Employee terminations
Restructuring Cost and Reserve [Line Items]
Total restructuring charges		49	0	770	65
Industrial | Other restructuring charges
Restructuring Cost and Reserve [Line Items]
Total restructuring charges		$ 124	$ 0	$ 374	$ 0

Debt - Carrying Amounts of Long

Debt - Carrying Amounts of Long-term Debt (Details) - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 29, 2018
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ (3,893)	$ (4,636)
Total debt	678,160	694,730
Less: Current maturities	(10,000)	(10,000)
Total long-term debt	668,160	684,730
Term Loan
Debt Instrument [Line Items]
Long-term debt, gross	147,500	155,000
Euro Senior Notes, Series A due 2023
Debt Instrument [Line Items]
Long-term debt, gross	128,002	133,417
Euro Senior Notes, Series B due 2028
Debt Instrument [Line Items]
Long-term debt, gross	103,932	108,330
U.S. Senior Notes, Series A due 2022
Debt Instrument [Line Items]
Long-term debt, gross	25,000	25,000
U.S. Senior Notes, Series B due 2027
Debt Instrument [Line Items]
Long-term debt, gross	100,000	100,000
U.S. Senior Notes, Series A due 2025
Debt Instrument [Line Items]
Long-term debt, gross	50,000	50,000
U.S. Senior Notes, Series B due 2030
Debt Instrument [Line Items]
Long-term debt, gross	125,000	125,000
Other
Debt Instrument [Line Items]
Long-term debt, gross	$ 2,619	$ 2,619

Debt - Narrative (Details)

Debt - Narrative (Details)

Jan. 16, 2018USD ($)

Oct. 13, 2017USD ($)advance

Mar. 04, 2016USD ($)

Sep. 28, 2019USD ($)

Sep. 29, 2018USD ($)

Sep. 28, 2019USD ($)

Sep. 29, 2018USD ($)

Nov. 15, 2017USD ($)series

Oct. 12, 2017USD ($)

Feb. 15, 2017USD ($)

Dec. 08, 2016USD ($)series

Dec. 08, 2016EUR (€)series

Debt Instrument [Line Items]

Cash paid during the period for interest

$ 6,400,000

$ 8,100,000

$ 17,900,000

$ 15,800,000

Credit Agreement

Debt Instrument [Line Items]

Debt term

5 years

Maximum borrowing capacity

$ 700,000,000

Additional uncommitted borrowing capacity

$ 300,000,000

150,000,000

Additional uncommitted borrowing capacity, minimum increments

$ 25,000,000

Number of advances | advance

2

Effective interest rate

3.54%

3.54%

Letter of credit outstanding (less than)

$ 100,000

$ 100,000

Credit Agreement | Minimum

Debt Instrument [Line Items]

Commitment fee

0.15%

Credit Agreement | Maximum

Debt Instrument [Line Items]

Commitment fee

0.25%

Credit Agreement | LIBOR | Minimum

Debt Instrument [Line Items]

Basis spread on variable rate

1.00%

Credit Agreement | LIBOR | Maximum

Debt Instrument [Line Items]

Basis spread on variable rate

2.00%

Credit Agreement | Base Rate | Minimum

Debt Instrument [Line Items]

Basis spread on variable rate

0.00%

Credit Agreement | Base Rate | Maximum

Debt Instrument [Line Items]

Basis spread on variable rate

1.00%

Credit Agreement | Revolving Credit Facility

Debt Instrument [Line Items]

Maximum borrowing capacity

$ 700,000,000

$ 575,000,000

$ 575,000,000

Remaining borrowing capacity

$ 416,500,000

416,500,000

Credit Agreement | Term Loan Credit Facility

Debt Instrument [Line Items]

Maximum borrowing capacity, credit facility

200,000,000

$ 125,000,000

Proceeds from issuance of debt

$ 75,000,000

$ 125,000,000

Quarterly payments, percentage of loan

1.25%

Periodic payment

$ 2,500,000

Repayments of debt

$ 7,500,000

Euro Senior Notes, Series A and B

Debt Instrument [Line Items]

Face amount of debt | €

€ 212,000,000

Number of series | series

2

2

2

Euro Senior Notes, Series A due 2023

Debt Instrument [Line Items]

Face amount of debt | €

€ 117,000,000

Stated interest rate

1.14%

1.14%

Euro Senior Notes, Series B due 2028

Debt Instrument [Line Items]

Face amount of debt | €

€ 95,000,000

Stated interest rate

1.83%

1.83%

U.S. Senior Notes, Series A and B

Debt Instrument [Line Items]

Face amount of debt

$ 125,000,000

U.S. Senior Notes, Series A

Debt Instrument [Line Items]

Face amount of debt

$ 25,000,000

Stated interest rate

3.03%

U.S. Senior Notes, Series B

Debt Instrument [Line Items]

Face amount of debt

$ 100,000,000

Stated interest rate

3.74%

US Senior Notes A and B Due 2025 and 2030

Debt Instrument [Line Items]

Face amount of debt

$ 175,000,000

U.S. Senior Notes, Series A due 2025

Debt Instrument [Line Items]

Face amount of debt

$ 50,000,000

Stated interest rate

3.48%

U.S. Senior Notes, Series B due 2030

Debt Instrument [Line Items]

Face amount of debt

$ 125,000,000

Stated interest rate

3.78%

Fair Value of Assets and Liab_3

Fair Value of Assets and Liabilities - Assets Measured at Fair Value (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Dec. 29, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment charges	$ 322	$ 1,125
Investments in equity securities	12,648		$ 10,312
Mutual funds	9,717		9,112
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities	12,648		10,312
Mutual funds	9,717		9,112
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities	0		0
Mutual funds	0		0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities	0		0
Mutual funds	0		$ 0
Other Expense (Income)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment charges	2,800
Investments in equity securities	$ 1,200

Fair Value of Assets and Liab_4

Fair Value of Assets and Liabilities - Carrying Value and Estimated Fair Value of Senior Notes (Details) - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 29, 2018
Carrying Value | Euro Senior Notes, Series A due 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	$ 128,002	$ 133,417
Carrying Value | Euro Senior Notes, Series B due 2028
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	103,933	108,330
Carrying Value | U.S. Senior Notes, Series A due 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	25,000	25,000
Carrying Value | U.S. Senior Notes, Series B due 2027
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	100,000	100,000
Carrying Value | U.S. Senior Notes, Series A due 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	50,000	50,000
Carrying Value | U.S. Senior Notes, Series B due 2030
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	125,000	125,000
Estimated Fair Value | Euro Senior Notes, Series A due 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	129,793	130,888
Estimated Fair Value | Euro Senior Notes, Series B due 2028
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	109,767	103,774
Estimated Fair Value | U.S. Senior Notes, Series A due 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	25,010	24,115
Estimated Fair Value | U.S. Senior Notes, Series B due 2027
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	103,179	94,458
Estimated Fair Value | U.S. Senior Notes, Series A due 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	50,918	47,434
Estimated Fair Value | U.S. Senior Notes, Series B due 2030
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt fair value	$ 128,681	$ 114,731

Benefit Plans - Narrative (Deta

Benefit Plans - Narrative (Details) $ in Millions	Sep. 28, 2019USD ($)
Retirement Benefits [Abstract]
Contributions expected	$ 2.3

Benefit Plans - Benefit Plan Ex

Benefit Plans - Benefit Plan Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Retirement Benefits [Abstract]
Service cost	$ 509	$ 533	$ 1,523	$ 1,599
Interest cost	777	501	2,374	1,503
Expected return on plan assets	(773)	(540)	(2,384)	(1,620)
Amortization of prior service	60	74	184	222
Net periodic benefit cost	$ 573	$ 568	$ 1,697	$ 1,704

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) - Schedule of Components of Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 28, 2019	Sep. 29, 2018
Other Comprehensive Income (Loss) [Line Items]
Pre-tax	$ (17,008)			$ (7,947)			$ (14,655)	$ (24,186)
Tax	18			0			29	(18)
Total change in other comprehensive income (loss)	(17,026)	$ (5,731)	$ 8,073	(7,947)	$ (15,942)	$ (279)	(14,684)	(24,168)
Pension and postretirement liability and reclassification adjustments
Other Comprehensive Income (Loss) [Line Items]
Pre-tax	155			(115)			278	630
Tax	18			0			29	(18)
Total change in other comprehensive income (loss)	137			(115)			249	648
Foreign currency translation adjustment
Other Comprehensive Income (Loss) [Line Items]
Pre-tax	(17,163)			(7,832)			(14,933)	(24,816)
Tax	0			0			0	0
Total change in other comprehensive income (loss)	$ (17,163)			$ (7,832)			$ (14,933)	$ (24,816)

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 28, 2019	Sep. 29, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	$ 1,509,942	$ 1,505,388	$ 1,478,342	$ 1,470,020	$ 1,441,974	$ 927,556	$ 1,478,342	$ 927,556
Cumulative effect adjustment								(9,795)
Other comprehensive income (loss), net of tax	(17,026)	(5,731)	8,073	(7,947)	(15,942)	(279)	(14,684)	(24,168)
Balance	1,472,212	1,509,942	1,505,388	1,519,396	1,470,020	1,441,974	1,472,212	1,519,396
Pension and postretirement liability and reclassification adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance			(9,959)			(10,836)	(9,959)	(10,836)
Cumulative effect adjustment								0
Other comprehensive income (loss), net of tax	137			(115)			249	648
Balance	(9,710)			(10,188)			(9,710)	(10,188)
Unrealized gain (loss) on investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance						9,795		9,795
Cumulative effect adjustment								(9,795)
Other comprehensive income (loss), net of tax								0
Balance				0				0
Foreign currency translation adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance			(87,965)			(62,627)	(87,965)	(62,627)
Cumulative effect adjustment								0
Other comprehensive income (loss), net of tax	(17,163)			(7,832)			(14,933)	(24,816)
Balance	(102,898)			(87,443)			(102,898)	(87,443)
Accumulated other comprehensive income (loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(95,582)	(89,851)	(97,924)	(89,684)	(73,742)	(63,668)	(97,924)	(63,668)
Other comprehensive income (loss), net of tax	(17,026)	(5,731)	8,073	(7,947)	(15,942)	(279)
Balance	$ (112,608)	$ (95,582)	$ (89,851)	$ (97,631)	$ (89,684)	$ (73,742)	$ (112,608)	$ (97,631)

Other Comprehensive Income (L_5

Other Comprehensive Income (Loss) - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service	$ 231,025	$ 259,597	$ 737,368	$ 817,983
Amortization of prior service | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service	$ 60	$ 74	$ 184	$ 222

Income Taxes (Details Textual)

Income Taxes (Details Textual)	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Income Tax Disclosure [Abstract]
Effective tax rate	13.90%	21.50%	17.70%	20.10%

Earnings Per Share - Narrative

Earnings Per Share - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018	Apr. 26, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Repurchases of common stock	$ 49,526	$ 31,955	$ 13,555
Share Repurchase Program
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Repurchase authorized (in shares)			1,000,000				1,000,000
Shares repurchased (in shares)	311,786				579,916
Repurchases of common stock	$ 49,500				$ 95,000
Employee Stock Option
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded (in shares)	205,516			38,082	147,090	39,446

Earnings Per Share - Computatio

Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 28, 2019	Sep. 29, 2018
Numerator:
Net income as reported	$ 35,647	$ 43,792	$ 36,989	$ 53,546	$ 42,326	$ 36,029	$ 116,428	$ 131,900
Weighted average shares outstanding
Basic (in shares)	24,482			25,109			24,646	24,817
Effect of dilutive securities (in shares)	202			362			248	395
Diluted (in shares)	24,684			25,471			24,894	25,212
Earnings Per Share:
Basic earnings per share (in dollars per share)	$ 1.46			$ 2.13			$ 4.72	$ 5.31
Diluted earnings per share (in dollars per share)	$ 1.44			$ 2.10			$ 4.68	$ 5.23

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	Mar. 25, 2019	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018	Dec. 29, 2018
Related Party Transaction [Line Items]
Cost method investments		$ 1.2		$ 1.2
Powersem
Related Party Transaction [Line Items]
Revenue from related parties		0.2	$ 0.2	0.4	$ 0.6
Purchase from related party		0.8	1.3	2.4	3.4
Receivable from related parties		0.1		0.1		$ 0.1
Payables to related parties		0.1		0.1		0.2
EB Tech
Related Party Transaction [Line Items]
Payables to related parties		0.1		0.1		0.1
Amount of transaction		0.1	0.1	0.3	0.3
ATEC
Related Party Transaction [Line Items]
Payables to related parties		0.2		0.2		$ 0.5
Amount of transaction		$ 1.7	$ 2.5	$ 5.5	$ 7.7
MWT
Related Party Transaction [Line Items]
Loss on disposal	$ 2.6
Powersem
Related Party Transaction [Line Items]
Ownership percentage		45.00%		45.00%
EB Tech
Related Party Transaction [Line Items]
Ownership percentage		19.00%		19.00%
ATEC
Related Party Transaction [Line Items]
Ownership percentage		24.00%		24.00%

Segment Information - Segment I

Segment Information - Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Segment Reporting Information [Line Items]
Net sales	$ 361,971	$ 439,191	$ 1,165,350	$ 1,316,187
Depreciation and amortization	23,088	26,258	69,056	76,060
Operating income (loss)	47,167	76,228	160,474	173,421
Interest expense	5,559	5,775	16,834	16,980
Foreign exchange loss (gain)	4,968	982	5,636	(6,372)
Other (income) expense, net	(4,764)	1,259	(3,406)	(2,362)
Income before income taxes	41,404	68,212	141,410	165,175
Electronics
Segment Reporting Information [Line Items]
Net sales	227,252	296,472	752,199	860,240
Automotive
Segment Reporting Information [Line Items]
Net sales	104,681	114,416	326,814	367,718
Industrial
Segment Reporting Information [Line Items]
Net sales	30,038	28,303	86,337	88,229
Operating Segments | Electronics
Segment Reporting Information [Line Items]
Net sales	227,252	296,472	752,199	860,240
Depreciation and amortization	14,960	15,898	45,031	45,227
Operating income (loss)	34,567	72,464	127,233	193,739
Operating Segments | Automotive
Segment Reporting Information [Line Items]
Net sales	104,681	114,416	326,814	367,718
Depreciation and amortization	7,067	5,891	20,848	17,830
Operating income (loss)	11,437	10,863	34,987	44,965
Operating Segments | Industrial
Segment Reporting Information [Line Items]
Net sales	30,038	28,303	86,337	88,229
Depreciation and amortization	1,061	1,364	3,177	4,291
Operating income (loss)	6,822	4,134	16,158	14,123
Corporate, Non-Segment | Other
Segment Reporting Information [Line Items]
Depreciation and amortization	0	3,105	0	8,712
Operating income (loss)	$ (5,659)	$ (11,233)	$ (17,904)	$ (79,406)

Segment Information - Narrative

Segment Information - Narrative (Details) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 28, 2019USD ($)	Sep. 29, 2018USD ($)	Jun. 30, 2018USD ($)	Sep. 28, 2019USD ($)segment	Sep. 29, 2018USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment				3
Restructuring charges	$ 2,215	$ 4,982		$ 10,633	$ 8,895
Impairment charges				322	1,125
Impairment charges	322	0		$ 322	1,125
Net sales | Geographic Concentration Risk | Other countries
Segment Reporting Information [Line Items]
Concentration risk (less than)				10.00%
Other | Operating Income (Loss)
Segment Reporting Information [Line Items]
Acquisition related costs		10,100			75,600
Inventory adjustment					36,900
Legal, accounting and other expenses	3,200	2,400		$ 6,900	16,100
Backlog amortization costs		3,100			8,700
Change in control expense					2,100
Restructuring charges	$ 2,500			$ 11,000
Impairment charges		400			1,600
Other restructuring			$ 1,100
Impairment charges		700			1,100
IXYS Corporation
Segment Reporting Information [Line Items]
Acquisition related costs					11,000
Allocated share based compensation					4,500
Restructuring charges		$ 4,600			$ 7,300

Segment Information - Revenues

Segment Information - Revenues and Long-lived Assets by Geographical Area (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018	Dec. 29, 2018
Segment Reporting Information [Line Items]
Net sales	$ 361,971	$ 439,191	$ 1,165,350	$ 1,316,187
Long-lived assets	329,792		329,792		$ 339,894
Additions to long-lived assets			47,375	55,946
United States
Segment Reporting Information [Line Items]
Net sales	105,292	125,867	340,811	386,980
Long-lived assets	56,790		56,790		58,691
Additions to long-lived assets			4,972	5,636
China
Segment Reporting Information [Line Items]
Net sales	101,960	117,813	316,553	352,097
Long-lived assets	88,386		88,386		95,806
Additions to long-lived assets			12,418	19,043
Mexico
Segment Reporting Information [Line Items]
Long-lived assets	73,350		73,350		70,495
Additions to long-lived assets			12,650	14,089
Germany
Segment Reporting Information [Line Items]
Long-lived assets	35,817		35,817		36,548
Additions to long-lived assets			4,335	5,917
Philippines
Segment Reporting Information [Line Items]
Long-lived assets	37,775		37,775		32,459
Additions to long-lived assets			9,546	6,133
Other countries
Segment Reporting Information [Line Items]
Net sales	154,719	$ 195,511	507,986	577,110
Long-lived assets	$ 37,674		37,674		$ 45,895
Additions to long-lived assets			$ 3,454	$ 5,128