Littelfuse (LFUS) 10-Q 2 May 18 2018 Q1 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 27, 2018
Document Information [Line Items]
Entity Registrant Name	LITTELFUSE INC /DE
Entity Central Index Key	889,331
Trading Symbol	lfus
Current Fiscal Year End Date	--12-29
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Common Stock, Shares Outstanding (in shares)		24,966,975
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Amendment Flag	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
ASSETS
Cash and cash equivalents	$ 412,458	$ 429,676
Short-term investments	37	35
Trade receivables, less allowances (March 31, 2018 - $33,746; December 30, 2017 - $27,516)	244,905	182,699
Inventories	263,969	140,789
Prepaid income taxes and income taxes receivable	3,899	1,689
Prepaid expenses and other current assets	47,794	37,452
Total current assets	973,062	792,340
Property, plant, and equipment:
Land	29,575	9,547
Buildings	118,170	86,599
Equipment	555,578	505,838
Accumulated depreciation and amortization	(366,118)	(351,407)
Net property, plant, and equipment	337,205	250,577
Intangible assets, net of amortization	405,406	203,850
Goodwill	840,574	453,414
Investments	31,128	10,993
Deferred income taxes	12,039	11,858
Other assets	28,096	17,070
Total assets	2,627,510	1,740,102
LIABILITIES AND EQUITY
Accounts payable	120,817	101,844
Accrued payroll	41,220	49,962
Accrued expenses	74,925	48,994
Accrued severance	1,367	1,459
Accrued income taxes	15,938	16,285
Current portion of long-term debt	10,111	6,250
Total current liabilities	264,378	224,794
Long-term debt, less current portion	743,437	489,361
Deferred income taxes	(60,525)	(17,069)
Accrued post-retirement benefits	35,817	18,742
Other long-term liabilities	81,379	62,580
Shareholders’ equity:
Common stock, par value $0.01 per share: 34,000,000 shares authorized; shares issued, March 31, 2018–24,936,931; December 30, 2017 –22,713,198	251	229
Treasury stock, at cost: 453,571 and 439,598 shares, respectively	(44,052)	(41,294)
Additional paid-in capital	800,614	310,012
Accumulated other comprehensive income	(73,742)	(63,668)
Retained earnings	758,766	722,140
Littelfuse, Inc. shareholders’ equity	1,441,837	927,419
Non-controlling interest	137	137
Total equity	1,441,974	927,556
Total liabilities and equity	$ 2,627,510	$ 1,740,102

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Trade receivables, allowances	$ 33,746	$ 27,516
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	34,000,000	34,000,000
Common stock, shares issued (in shares)	24,936,931	22,713,198
Treasury stock, shares (in shares)	453,571	439,598

Condensed Consolidated Statemen

Condensed Consolidated Statements of Net Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Net sales	$ 417,813	$ 285,441
Cost of sales	268,190	171,791
Gross profit	149,623	113,650
Selling, general, and administrative expenses	77,514	46,703
Research and development expenses	22,540	12,151
Amortization of intangibles	11,998	5,944
Total operating expenses	112,052	64,798
Operating income	37,571	48,852
Interest expense	5,423	3,120
Foreign exchange gain	(10,555)	(1,557)
Other (income) expense, net	(1,943)	(139)
Income before income taxes	44,646	47,428
Income taxes	8,617	8,537
Net income	$ 36,029	$ 38,891
Income per share:
Basic (in dollars per share)	$ 1.48	$ 1.71
Diluted (in dollars per share)	$ 1.45	$ 1.69
Weighted-average shares and equivalent shares outstanding:
Basic (in shares)	24,339	22,748
Diluted (in shares)	24,775	22,989
Cash dividends declared per common share (in dollars per share)	$ 0.37	$ 0.33

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Net income	$ 36,029	$ 38,891
Other comprehensive income (loss):
Pension and postemployment liability adjustments (net of tax expense (benefit) of ($60) and ($32), respectively)	(188)	(181)
Pension and postemployment reclassification adjustments (net of tax (benefit) expense of ($5) and $36, respectively)	185	(101)
Unrealized (loss) gain on investments		947
Foreign currency translation adjustments	(276)	4,962
Comprehensive income	$ 35,750	$ 44,518

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parentheticals) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Pension and postemployment liability adjustments, tax	$ (60)	$ (32)
Pension and postemployment reclassification adjustments, tax	$ (5)	$ 36

Condensed Consolidated Stateme7

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Operating activities
Net income	$ 36,029	$ 38,891
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	11,614	9,128
Amortization of intangibles	11,998	5,944
Provision for bad debts	(13)	351
Non-cash inventory charges	17,896
Unrealized gain on investments	(1,864)
Loss on sale of property, plant, and equipment	99	600
Stock-based compensation	8,714	3,583
Deferred income taxes	842	616
Changes in operating assets and liabilities:
Accounts receivable	(8,417)	(11,267)
Inventories	(269)	(3,296)
Accounts payable	2,990	(3,295)
Accrued expenses (including post-retirement)	12,573	4,140
Accrued payroll and severance	(18,607)	(20,221)
Accrued taxes	(1,174)	(220)
Prepaid expenses and other	(3,143)	(2,011)
Net cash provided by operating activities	69,268	22,943
Investing activities
Acquisitions of businesses, net of cash acquired	(306,487)	(14,172)
Proceeds from maturities of short-term investments		3,739
Decrease in entrusted loan		655
Purchases of property, plant, and equipment	(17,909)	(12,377)
Proceeds from sale of property, plant, and equipment	19	57
Net cash used in investing activities	(324,377)	(22,098)
Financing activities:
Proceeds of revolving credit facility	50,000
Proceeds of term loan	75,000
Proceeds of senior notes payable	175,000	125,000
Payments of term loan	(2,500)	(1,563)
Payments of revolving credit facility	(47,000)	(112,500)
Net (payments) proceeds related to stock-based award activities	116	(199)
Proceeds (payments) from entrusted loan		(655)
Debt issuance costs	(878)	(71)
Cash dividends paid	(9,198)	(7,472)
Net cash provided by financing activities	240,308	2,938
Effect of exchange rate changes on cash and cash equivalents	(2,417)	(928)
Increase (decrease) in cash and cash equivalents	(17,218)	2,855
Cash and cash equivalents at beginning of year	429,676	275,124
Cash and cash equivalents at end of year	$ 412,458	$ 277,979

Note 1 - Summary of Significant

Note 1 - Summary of Significant Accounting Policies and Other Information	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Significant Accounting Policies [Text Block]	1. Nature of Operations Littelfuse, Inc. and subsidiaries (the “Company”) is a global leader in circuit protection products with advancing platforms in power control and sensor technologies, serving customers in the electronics, automotive, and industrial markets. With a diverse and extensive product portfolio of fuses, semiconductors, polymers, ceramics, relays and sensors, the Company works with its customers to build safer, more reliable and more efficient products for the connected world in virtually every market that uses electrical energy, ranging across consumer electronics, IT and telecommunication applications, industrial electronics, automobiles and other transportation, and heavy industrial applications. The Company has a network of global engineering centers and labs that develop new products and product enhancements, provides customer application support and test products for safety, reliability, and regulatory compliance. 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 10 X. not 10 December 30, 2017, not Revenue Recognition Adoption On December 31, 2017, not Revenue Disaggregation The following table disaggregates the Company’s revenue by primary business units for the three March 31, 2018: (in thousands) Electronics Segment Automotive Segment Industrial Segment Total Electronics – Passive Products and Sensors $ 114,495 $ — $ — $ 114,495 Electronics - Semiconductor 149,916 — — 149,916 Passenger Car Products — 63,580 — 63,580 Automotive Sensors — 31,323 — 31,323 Commercial Vehicle Products — 31,228 — 31,228 Industrial Products — — 27,271 27,271 Total $ 264,411 $ 126,131 $ 27,271 $ 417,813 See Note 12, Segment Information 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 may third The Company has elected the practical expedient under ASC 340 40 25 4 one 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 606 10 32 18 not 606 10 25 18B 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 March 2017, No. 2017 07 715 No. 2017 07 first 2018 December 31, 2017. In January 2016, No. 2016 01, December 31, 2017, $9.8 three March 31, 2018, $1.9 In May 2014, No. 2014 09, 606 605, two one one December 31, 2017 no not Revenue Recognition In October 2016, No. 2016 16, 740 December 31, 2017 not Recently Issued Accounting Standards In February 2016, No. 2016 02, 842 twelve December 15, 2018, first 2019. 2016 02. In January 2018, not not In February 2018, No. 2018 02 220 not 2018 02 first 2019; 2018 02

Note 2 - Acquisitions

Note 2 - Acquisitions	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Mergers, Acquisitions and Dispositions Disclosures [Text Block]	2 . Acquisitions The Company accounts for acquisitions using the acquisition method in accordance with ASC 805, IXYS Corporation On January 17, 2018, 3,500 Upon completion of the acquisition, at IXYS stockholders’ election and subject to proration, each share of IXYS common stock, par value $0.01 $23.00 0.1265 $0.01 0.1265, 0.1265, Based on the $207.5 January 17, 2018, $814.8 $380.5 $434.2 $41.7 $856.5 The total purchase price of $856.5 not 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 $ 154,254 Property, plant, and equipment 76,580 Intangible assets 211,600 Goodwill 381,599 Other non-current assets 31,570 Other non-current liabilities (76,815 ) $ 778,788 Included in IXYS’s current assets, net was approximately $49.1 not Included in the Company’s Condensed Consolidated Statements of Net Income for the three March 31, 2018 $86.3 $17.8 January 17, 2018 $5.9 three March 31, 2018 $4.5 As required by purchase accounting rules, the Company recorded a $36.9 first second 2018, three March 31, 2018, $17.9 During the three March 31, 2018, $10.2 selling, general, and administrative expenses 2017 U.S. Sensor On July 7, 2017, $24.3 fourth 2017, The following table summarizes the purchase price allocation of the fair value of assets acquired and liabilities assumed in the U.S. Sensor acquisition: (in thousands) Purchase Price Allocation Total purchase consideration: Cash $ 24,340 Allocation of consideration to assets acquired and liabilities assumed: Current assets, net $ 4,635 Patented and unpatented technologies 1,090 Trademarks and tradenames 200 Non-compete agreement 50 Customer relationships 2,830 Goodwill 16,075 Current liabilities (540 ) $ 24,340 Included in U.S. Sensor’s current assets, net was approximately $1.5 As required by purchase accounting rules, the Company recorded a $1.6 third 2017, Monolith In December 2015, $3.5 12% $3.5 December 31, 2016. On February 28, 2017, 62% $15 first 2018, April 2018 19% $5 19% $0.5 $5 no June 30, 2019. The additional investment, in the first 2017, $3.5 no $3.5 $14.2 $9.0 $26.7 Commencing March 1, 2017, January 1, 2017, not The following table summarizes the purchase price allocation of the fair value of assets acquired and liabilities assumed in the Monolith acquisition: (in thousands) Purchase Price Allocation Total purchase consideration: Original investment $ 3,500 Cash, net of cash acquired 14,172 Non-cash, fair value of commitment to purchase non-controlling interest 9,000 Total purchase consideration $ 26,672 Allocation of consideration to assets acquired and liabilities assumed: Current assets, net $ 891 Property, plant, and equipment 789 Patented and unpatented technologies 6,720 Non-compete agreement 140 Goodwill 20,641 Current liabilities (639 ) Other non-current liabilities (1,870 ) $ 26,672 Included in Monolith’s current assets, net was approximately $0.7 not 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. not not not January 1, 2017 For the Three Months Ended (in thousands , except per share amounts ) March 31, 2018 April 1 , 2017 Net sales $ 434,526 $ 368,813 Income before income taxes 81,924 11,021 Net income 63,933 17,462 Net income per share — basic 2.57 0.70 Net income per share — diluted 2.53 0.69 Pro forma results presented above primarily reflect the following adjustments: For the Three Months Ended (in thousands) March 31, 2018 April 1, 2017 Amortization (a) $ 1,902 $ (6,276 ) Depreciation — (94 ) Transaction costs (b) 9,976 (9,976 ) Amortization of inventory step-up (c) 17,896 (22,156 ) Stock compensation (d) 4,479 (5,013 ) Interest expense (e) — (2,582 ) Income tax impact of above items (7,701 ) 15,374 (a) The amortization adjustment for the three March 31, 2018 twelve 2017 three April 1, 2017 (b) The transaction cost adjustments reflect the reversal of certain bank and attorney fees from the three March 31, 2018 three April 1, 2017. (c) The amortization of inventory step-up adjustment reflects the reversal of the amount recognized during the three March 31, 2018 three April 1, 2017. five (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 three March 31, 2018. three April 1, 2017 (e) The interest expense adjustment reflects incremental interest expense related to the financing of the transaction.

Note 3 - Inventories

Note 3 - Inventories	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Inventory Disclosure [Text Block]	3 . Inventories The components of inventories at March 31, 2018 December 30, 2017 (in thousands) March 31, 2018 December 30, 2017 Raw materials $ 66,259 $ 39,030 Work in process 96,826 27,454 Finished goods 100,884 74,305 Total $ 263,969 $ 140,789

Note 4 - Goodwill and Other Int

Note 4 - Goodwill and Other Intangible Assets	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Goodwill and Intangible Assets Disclosure [Text Block]	4. The amounts for goodwill and changes in the carrying value by segment for the three March 31, 2018 (in thousands) Electronics Automotive Industrial Total As of December 30, 2017 $ 278,959 $ 135,829 $ 38,626 $ 453,414 Additions (a ) 381,599 — — 381,599 Currency translation 2,455 3,195 (89 ) 5,561 As of March 31, 2018 $ 663,013 $ 139,024 $ 38,537 $ 840,574 (a) The additions resulted from the acquisition of IXYS. The components of other intangible assets at March 31, 2018 (in thousands, except weighted average useful life) Weighted Average Useful Life Gross Carrying Value Accumulated Amortization Net Book Value Patents, licenses and software 10.6 $ 193,622 $ 64,012 $ 129,610 Distribution network 12.6 44,473 33,434 11,039 Customer relationships, trademarks, and tradenames 18.1 314,452 59,591 254,861 Order backlog 1.0 12,400 2,504 9,896 Total $ 564,947 $ 159,541 $ 405,406 During the three March 31, 2018, $211.6 (in thousands , except weighted average useful life ) Weighted Average Useful Life Amount Patents, licenses and software 8.0 $ 51,500 Customer relationships, trademarks,and tradenames 17.2 147,700 Order backlog 1.0 12,400 Total $ 211,600 During the three March 31, 2018 April 1, 2017, $12.0 $5.9 Estimated annual amortization expense related to intangible assets with definite lives as of March 31, 2018 (in thousands) Amount 2018 $ 54,938 2019 42,005 2020 41,747 2021 39,928 2022 38,918 2023 and thereafter 197,914 Total $ 415,450

Note 5 - Debt

Note 5 - Debt	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Debt Disclosure [Text Block]	5 . Debt The carrying amounts of debt at March 31, 2018 December 30, 2017 (in thousands ) March 31, 2018 December 30, 2017 Revolving Credit Facility $ 3,000 $ — Term Loan 195,000 122,500 Euro Senior Notes, Series A due 2023 144,041 139,623 Euro Senior Notes, Series B due 2028 116,956 113,369 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 — U.S. Senior Notes, Series B due 2030 125,000 — Other 111 — Unamortized debt issuance costs (5,560 ) (4,881 ) Total debt 753,548 495,611 Less: Current maturities (10,111 ) (6,250 ) Total long-term debt $ 743,437 $ 489,361 Revolving Credit Facility / Term Loan On March 4, 2016, five $700.0 $575.0 $125.0 $150.0 $25.0 $1.6 March 31, 2018 $3.1 June 30, 2018 December 31, 2020 March 4, 2021. On October 13, 2017, $575.0 $700.0 $125.0 $200.0 March 4, 2021 October 13, 2022. $300.0 may two first $125.0 October 13, 2017 second $75.0 January 16, 2018. 1.25% $2.5 second January 16, 2018) October 13, 2022. Outstanding borrowings under the Credit Agreement bear interest, at the Company’s option, at either LIBOR, fixed for interest periods of one, two, three six 1.00% 2.00%, 0.00% 1.00%, 0.15% 0.25%, 3.13% March 31, 2018. As of March 31, 2018, $0.1 $696.9 March 31, 2018, Senior Notes On December 8, 2016, €212 two December 8, 2016 €117 1.14% December 8, 2023 ( 2023” €95 1.83% December 8, 2028 ( 2028” June 8 December 8, June 8, 2017. On December 8, 2016, $125 two February 15, 2017, $25 3.03% February 15, 2022 ( 2022” $100 3.74% February 15, 2027 ( 2027” 2022 2027” 2022 2027 February 15 August 15, August 15, 2017. On November 15, 2017, $175 two January 16, 2018, $50 3.48% February 15, 2025 ( 2025” $125 3.78% February 15, 2030 ( 2030” 2025 2030” 2022 2027, 2025 2030 February 15 August 15, August 15, 2018. The Senior Notes have not 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 March 31, 2018, The Company may

Note 6 - Fair Value of Assets a

Note 6 - Fair Value of Assets and Liabilities	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Fair Value Disclosures [Text Block]	6 . Fair Value of Assets and Liabilities For assets and liabilities measured at fair value on a recurring and nonrecurring basis, a three Level 1 Level 2 not Level 3 one 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 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 There were no March 31, 2018 March 31, 2018 December 30, 2017, not The following table presents assets measured at fair value by classification within the fair value hierarchy as of March 31, 2018: Fair Value Measurements Using (in thousands ) Quoted Prices in Significant Significant Total Investments in equity securities $ 14,754 $ — $ — $ 14,754 Mutual funds 9,852 — — 9,852 The following table presents assets measured at fair value by classification within the fair value hierarchy as of December 30, 2017: Fair Value Measurements Using (in thousands ) Quoted Prices in Significant Significant Total Investments in equity securities $ 10,993 $ — $ — $ 10,993 Mutual funds 7,962 — — 7,962 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 March 31, 2018 December 30, 2017, 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 30, 2017 December 31, 2016 March 31 , 201 8 December 30 , 201 7 (in thousands ) Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Euro Senior Notes, Series A due 2023 $ 144,041 $ 142,038 $ 139,623 $ 138,294 Euro Senior Notes, Series B due 2028 116,956 113,953 113,369 111,579 USD Senior Notes, Series A due 2022 25,000 24,301 25,000 24,737 USD Senior Notes, Series B due 2027 100,000 96,475 100,000 99,992 USD Senior Notes, Series A due 2025 50,000 48,081 — — USD Senior Notes, Series B due 2030 125,000 118,303 — —

Note 7 - Benefit Plans

Note 7 - Benefit Plans	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Pension and Other Postretirement Benefits Disclosure [Text Block]	7 . Benefit Plans The Company has company-sponsored defined benefit pension plans covering employees in the U.K., Germany, the Philippines, China, Japan, 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 costs, expected return on plan assets, and amortization, net within Other (income) expense, net three March 31, 2018 April 1, 2017 For the Three Months Ended (in thousands) March 31 , 201 8 April 1 , 201 7 Components of net periodic benefit cost: Service cost $ 533 $ 408 Interest cost 501 360 Expected return on plan assets (540 ) (476 ) Amortization, net 74 84 Net periodic benefit cost $ 568 $ 376 The Company expects to make approximately $2.3 2018.

Note 8 - Shareholders' Equity

Note 8 - Shareholders' Equity	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Stockholders' Equity Note Disclosure [Text Block]	8 . Shareholders’ Equity The following table sets forth the changes in shareholders’ equity for the three March 31, 2018: (in thousands ) Littelfuse, Inc. Shareholders’ Equity Non- controlling Interest Total Balance at December 30, 2017 $ 927,419 $ 137 $ 927,556 Net income 36,029 — 36,029 Other comprehensive income (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 (a) 472,301 — 472,301 Cash dividends paid ($0.37 per share) (9,198 ) — (9,198 ) Non-controlling interest — — — Balance at March 31, 2018 $ 1,441,837 $ 137 $ 1,441,974 (a) The issuance of common stock ( 2,092,491 three March 31, 2018 2, Acquisitions The following table sets forth the changes in the components of Accumulated Other Comprehensive Income (Loss) by component for the three March 31, 2018: (in thousands ) Pension and postretirement liability and reclassification adjustments (a) Unrealized g ain /(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 (b) — (9,795 ) — (9,795 ) Activity in the period (3 ) — (276 ) (279 ) Balance at March 31, 2018 $ (10,839 ) $ — $ (62,903 ) $ (73,742 ) (a) The balances at March 31, 2018 December 30, 2017 $0.2 $1.4 (b) The Company adopted ASU 2016 01 December 31, 2018 $9.8 1, Summary of Significant Accounting Policies and Other Information

Note 9 - Income Taxes

Note 9 - Income Taxes	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Income Tax Disclosure [Text Block]	9 . Income Taxes The effective tax rate for the first 2018 19.3% 18.0% first 2017. first 2017 35% On December 22, 2017, 35% 21%, one 2017 2018 In accordance with the guidance provided in SEC Staff Accounting Bulletin (“SAB”) No. 118, fourth 2017 $47 $49 $2 not first 2018. $10 No. 118. may may The Company recognized deferred tax liabilities of $12.0 $11.8 $0.2 December 30, 2017 not may no December 30, 2017, no first 2018. One of the base broadening provisions of the Tax Act is commonly referred to as the “GILTI” provisions. In accordance with guidance issued by the FASB staff, the Company has not 118. not first 2018. Although certain administrative guidance has been issued, the appropriate application of many provisions of the Tax Act remain uncertain. The Company used its best judgement as to the application of these provisions in determining its income tax expense for the first 2018.

Note 10 - Earnings Per Share

Note 10 - Earnings Per Share	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Earnings Per Share [Text Block]	10 . Earnings Per Share The following table sets forth the computation of basic and diluted earnings per share: For the Three Months Ended (in thousands , except per share amounts ) March 31 , 201 8 April 1 , 201 7 Numerator: Net income as reported $ 36,029 $ 38,891 Denominator: Weighted average shares outstanding Basic 24,339 22,748 Effect of dilutive securities 436 241 Diluted 24,775 22,989 Earnings Per Share: Basic earnings per share $ 1.48 $ 1.71 Diluted earnings per share $ 1.45 $ 1.69 No three March 31, 2018 April 1, 2017,

Note 11 - Related Party Transac

Note 11 - Related Party Transactions	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Related Party Transactions Disclosure [Text Block]	11 . Related Party Transactions As a result of the Company’s acquisition of IXYS, the Company has equity ownerships in various investments that are accounted for under the equity method. The following is a description of the investments and related party transactions. Powersem GmbH : 45% three March 31, 2018, $0.1 three March 31, 2018, $1.1 March 31, 2018, $0.1 $0.3 EB Tech Ltd.: 20% three March 31, 2018 $0.1 March 31, 2018, Automated Technology, Inc. 24% three March 31, 2018, $2.4 March 31, 2018, $0.8

Note 12 - Segment Information

Note 12 - Segment Information	3 Months Ended
	Mar. 31, 2018
Notes to Financial Statements
Segment Reporting Disclosure [Text Block]	1 2 . 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 not 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 not not not not not not one may ● Electronics Segment one ● Automotive Segment: ● Industrial Segment: Segment information is summarized as follows: For the Three Months Ended (in thousands ) March 31 , 201 8 April 1 , 201 7 Net sales Electronics $ 264,411 $ 153,767 Automotive 126,131 107,839 Industrial 27,271 23,835 Total net sales $ 417,813 $ 285,441 Depreciation and amortization Electronics $ 13,678 $ 8,387 Automotive 5,970 5,371 Industrial 1,460 1,314 Other 2,504 — Total depreciation and amortization $ 23,612 $ 15,072 Operating income (loss) Electronics $ 53,964 $ 35,206 Automotive 18,390 15,065 Industrial 4,709 106 Other (a) (39,492 ) (1,525 ) Total operating income 37,571 48,852 Interest expense 5,423 3,120 Foreign exchange loss (gain) (10,555 ) (1,557 ) Other income, net (1,943 ) (139 ) Income before income taxes $ 44,646 $ 47,428 (a) For the first 2018, $39.5 $38.6 2018 $18.4 $17.9 $16.1 $1.6 $2.5 $0.8 $0.5 $0.3 $0.1 2017 For the first 2017, $1.5 2016 The Company’s net sales by country were as follows: For the Three Months Ended (in thousands ) March 31, 2018 April 1, 2017 Net sales United States $ 123,877 $ 86,658 China (a) 106,508 78,219 Other countries ( b ) 187,428 120,564 Total net sales $ 417,813 $ 285,441 (a) Includes mainland China, Taiwan, and Hong Kong. (b) Each country included in Other countries are less than 10% The Company’s long-lived assets by country, as of March 31, 2018 April 1, 2017, (in thousands ) March 31, 2018 December 30, 2017 Long-lived assets United States $ 49,132 $ 23,490 China (a) 91,676 86,866 Mexico 64,176 62,510 Germany 36,232 1,082 Philippines 30,734 31,129 Other countries 65,255 45,500 Total long-lived assets $ 337,205 $ 250,577 The Company’s additions to long-lived assets by country were as follows: For the Three Months Ended (in thousands ) March 31, 2018 April 1, 2017 Additions to long-lived assets United States $ 2,909 $ 332 China (a) 5,144 2,392 Mexico 3,310 6,978 Germany 3,038 45 Philippines 2,162 855 Other countries 1,346 1,775 Total additions to long-lived assets $ 17,909 $ 12,377

Significant Accounting Policies

Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Accounting, Policy [Policy Text Block]	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 10 X. not 10 December 30, 2017, not
Revenue from Contract with Customer [Policy Text Block]	Revenue Recognition Adoption On December 31, 2017, not Revenue Disaggregation The following table disaggregates the Company’s revenue by primary business units for the three March 31, 2018: (in thousands) Electronics Segment Automotive Segment Industrial Segment Total Electronics – Passive Products and Sensors $ 114,495 $ — $ — $ 114,495 Electronics - Semiconductor 149,916 — — 149,916 Passenger Car Products — 63,580 — 63,580 Automotive Sensors — 31,323 — 31,323 Commercial Vehicle Products — 31,228 — 31,228 Industrial Products — — 27,271 27,271 Total $ 264,411 $ 126,131 $ 27,271 $ 417,813 See Note 12, Segment Information
Revenue Recognition, Policy [Policy Text Block]	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 may third The Company has elected the practical expedient under ASC 340 40 25 4 one
Revenue Recognition And Billing [Policy Text Block]	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 606 10 32 18 not 606 10 25 18B
Revenue Recognition, Sales Returns [Policy Text Block]	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.
Revenue Recognition Return to Stock [Policy Text Block]	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.
Revenue Recognition, Rebates [Policy Text Block]	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.
New Accounting Pronouncements, Policy [Policy Text Block]	Recently Adopted Accounting Standards In March 2017, No. 2017 07 715 No. 2017 07 first 2018 December 31, 2017. In January 2016, No. 2016 01, December 31, 2017, $9.8 three March 31, 2018, $1.9 In May 2014, No. 2014 09, 606 605, two one one December 31, 2017 no not Revenue Recognition In October 2016, No. 2016 16, 740 December 31, 2017 not Recently Issued Accounting Standards In February 2016, No. 2016 02, 842 twelve December 15, 2018, first 2019. 2016 02. In January 2018, not not In February 2018, No. 2018 02 220 not 2018 02 first 2019; 2018 02

Note 1 - Summary of Significa21

Note 1 - Summary of Significant Accounting Policies and Other Information (Tables)	3 Months Ended
	Mar. 31, 2018
Notes Tables
Disaggregation of Revenue [Table Text Block]	(in thousands) Electronics Segment Automotive Segment Industrial Segment Total Electronics – Passive Products and Sensors $ 114,495 $ — $ — $ 114,495 Electronics - Semiconductor 149,916 — — 149,916 Passenger Car Products — 63,580 — 63,580 Automotive Sensors — 31,323 — 31,323 Commercial Vehicle Products — 31,228 — 31,228 Industrial Products — — 27,271 27,271 Total $ 264,411 $ 126,131 $ 27,271 $ 417,813

Note 2 - Acquisitions (Tables)

Note 2 - Acquisitions (Tables)	3 Months Ended
	Mar. 31, 2018
Notes Tables
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]	(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 $ 154,254 Property, plant, and equipment 76,580 Intangible assets 211,600 Goodwill 381,599 Other non-current assets 31,570 Other non-current liabilities (76,815 ) $ 778,788 (in thousands) Purchase Price Allocation Total purchase consideration: Cash $ 24,340 Allocation of consideration to assets acquired and liabilities assumed: Current assets, net $ 4,635 Patented and unpatented technologies 1,090 Trademarks and tradenames 200 Non-compete agreement 50 Customer relationships 2,830 Goodwill 16,075 Current liabilities (540 ) $ 24,340 (in thousands) Purchase Price Allocation Total purchase consideration: Original investment $ 3,500 Cash, net of cash acquired 14,172 Non-cash, fair value of commitment to purchase non-controlling interest 9,000 Total purchase consideration $ 26,672 Allocation of consideration to assets acquired and liabilities assumed: Current assets, net $ 891 Property, plant, and equipment 789 Patented and unpatented technologies 6,720 Non-compete agreement 140 Goodwill 20,641 Current liabilities (639 ) Other non-current liabilities (1,870 ) $ 26,672
Business Acquisition, Pro Forma Information [Table Text Block]	For the Three Months Ended (in thousands , except per share amounts ) March 31, 2018 April 1 , 2017 Net sales $ 434,526 $ 368,813 Income before income taxes 81,924 11,021 Net income 63,933 17,462 Net income per share — basic 2.57 0.70 Net income per share — diluted 2.53 0.69
Business Acquisition, Pro Forma Information, Nonrecurring Adjustments [Table Text Block]	For the Three Months Ended (in thousands) March 31, 2018 April 1, 2017 Amortization (a) $ 1,902 $ (6,276 ) Depreciation — (94 ) Transaction costs (b) 9,976 (9,976 ) Amortization of inventory step-up (c) 17,896 (22,156 ) Stock compensation (d) 4,479 (5,013 ) Interest expense (e) — (2,582 ) Income tax impact of above items (7,701 ) 15,374

Note 3 - Inventories (Tables)

Note 3 - Inventories (Tables)	3 Months Ended
	Mar. 31, 2018
Notes Tables
Schedule of Inventory, Current [Table Text Block]	(in thousands) March 31, 2018 December 30, 2017 Raw materials $ 66,259 $ 39,030 Work in process 96,826 27,454 Finished goods 100,884 74,305 Total $ 263,969 $ 140,789

Note 4 - Goodwill and Other I24

Note 4 - Goodwill and Other Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2018
Notes Tables
Schedule of Goodwill [Table Text Block]	(in thousands) Electronics Automotive Industrial Total As of December 30, 2017 $ 278,959 $ 135,829 $ 38,626 $ 453,414 Additions (a ) 381,599 — — 381,599 Currency translation 2,455 3,195 (89 ) 5,561 As of March 31, 2018 $ 663,013 $ 139,024 $ 38,537 $ 840,574
Schedule of Finite-Lived Intangible Assets [Table Text Block]	(in thousands, except weighted average useful life) Weighted Average Useful Life Gross Carrying Value Accumulated Amortization Net Book Value Patents, licenses and software 10.6 $ 193,622 $ 64,012 $ 129,610 Distribution network 12.6 44,473 33,434 11,039 Customer relationships, trademarks, and tradenames 18.1 314,452 59,591 254,861 Order backlog 1.0 12,400 2,504 9,896 Total $ 564,947 $ 159,541 $ 405,406 (in thousands , except weighted average useful life ) Weighted Average Useful Life Amount Patents, licenses and software 8.0 $ 51,500 Customer relationships, trademarks,and tradenames 17.2 147,700 Order backlog 1.0 12,400 Total $ 211,600
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	(in thousands) Amount 2018 $ 54,938 2019 42,005 2020 41,747 2021 39,928 2022 38,918 2023 and thereafter 197,914 Total $ 415,450

Note 5 - Debt (Tables)

Note 5 - Debt (Tables)	3 Months Ended
	Mar. 31, 2018
Notes Tables
Schedule of Long-term Debt Instruments [Table Text Block]	(in thousands ) March 31, 2018 December 30, 2017 Revolving Credit Facility $ 3,000 $ — Term Loan 195,000 122,500 Euro Senior Notes, Series A due 2023 144,041 139,623 Euro Senior Notes, Series B due 2028 116,956 113,369 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 — U.S. Senior Notes, Series B due 2030 125,000 — Other 111 — Unamortized debt issuance costs (5,560 ) (4,881 ) Total debt 753,548 495,611 Less: Current maturities (10,111 ) (6,250 ) Total long-term debt $ 743,437 $ 489,361

Note 6 - Fair Value of Assets26

Note 6 - Fair Value of Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2018
Notes Tables
Fair Value, Assets Measured on Recurring Basis [Table Text Block]	Fair Value Measurements Using (in thousands ) Quoted Prices in Significant Significant Total Investments in equity securities $ 14,754 $ — $ — $ 14,754 Mutual funds 9,852 — — 9,852 Fair Value Measurements Using (in thousands ) Quoted Prices in Significant Significant Total Investments in equity securities $ 10,993 $ — $ — $ 10,993 Mutual funds 7,962 — — 7,962
Fair Value, by Balance Sheet Grouping [Table Text Block]	March 31 , 201 8 December 30 , 201 7 (in thousands ) Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Euro Senior Notes, Series A due 2023 $ 144,041 $ 142,038 $ 139,623 $ 138,294 Euro Senior Notes, Series B due 2028 116,956 113,953 113,369 111,579 USD Senior Notes, Series A due 2022 25,000 24,301 25,000 24,737 USD Senior Notes, Series B due 2027 100,000 96,475 100,000 99,992 USD Senior Notes, Series A due 2025 50,000 48,081 — — USD Senior Notes, Series B due 2030 125,000 118,303 — —

Note 7 - Benefit Plans (Tables)

Note 7 - Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2018
Notes Tables
Schedule of Net Benefit Costs [Table Text Block]	For the Three Months Ended (in thousands) March 31 , 201 8 April 1 , 201 7 Components of net periodic benefit cost: Service cost $ 533 $ 408 Interest cost 501 360 Expected return on plan assets (540 ) (476 ) Amortization, net 74 84 Net periodic benefit cost $ 568 $ 376

Note 8 - Shareholders' Equity (

Note 8 - Shareholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2018
Notes Tables
Schedule of Stockholders Equity [Table Text Block]	(in thousands ) Littelfuse, Inc. Shareholders’ Equity Non- controlling Interest Total Balance at December 30, 2017 $ 927,419 $ 137 $ 927,556 Net income 36,029 — 36,029 Other comprehensive income (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 (a) 472,301 — 472,301 Cash dividends paid ($0.37 per share) (9,198 ) — (9,198 ) Non-controlling interest — — — Balance at March 31, 2018 $ 1,441,837 $ 137 $ 1,441,974
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	(in thousands ) Pension and postretirement liability and reclassification adjustments (a) Unrealized g ain /(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 (b) — (9,795 ) — (9,795 ) Activity in the period (3 ) — (276 ) (279 ) Balance at March 31, 2018 $ (10,839 ) $ — $ (62,903 ) $ (73,742 )

Note 10 - Earnings Per Share (T

Note 10 - Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2018
Notes Tables
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	For the Three Months Ended (in thousands , except per share amounts ) March 31 , 201 8 April 1 , 201 7 Numerator: Net income as reported $ 36,029 $ 38,891 Denominator: Weighted average shares outstanding Basic 24,339 22,748 Effect of dilutive securities 436 241 Diluted 24,775 22,989 Earnings Per Share: Basic earnings per share $ 1.48 $ 1.71 Diluted earnings per share $ 1.45 $ 1.69

Note 12 - Segment Information (

Note 12 - Segment Information (Tables)	3 Months Ended
	Mar. 31, 2018
Notes Tables
Schedule of Segment Reporting Information, by Segment [Table Text Block]	For the Three Months Ended (in thousands ) March 31 , 201 8 April 1 , 201 7 Net sales Electronics $ 264,411 $ 153,767 Automotive 126,131 107,839 Industrial 27,271 23,835 Total net sales $ 417,813 $ 285,441 Depreciation and amortization Electronics $ 13,678 $ 8,387 Automotive 5,970 5,371 Industrial 1,460 1,314 Other 2,504 — Total depreciation and amortization $ 23,612 $ 15,072 Operating income (loss) Electronics $ 53,964 $ 35,206 Automotive 18,390 15,065 Industrial 4,709 106 Other (a) (39,492 ) (1,525 ) Total operating income 37,571 48,852 Interest expense 5,423 3,120 Foreign exchange loss (gain) (10,555 ) (1,557 ) Other income, net (1,943 ) (139 ) Income before income taxes $ 44,646 $ 47,428
Schedule of Disclosure on Geographic Areas, Long-Lived Assets in Individual Foreign Countries by Country [Table Text Block]	For the Three Months Ended (in thousands ) March 31, 2018 April 1, 2017 Net sales United States $ 123,877 $ 86,658 China (a) 106,508 78,219 Other countries ( b ) 187,428 120,564 Total net sales $ 417,813 $ 285,441 (in thousands ) March 31, 2018 December 30, 2017 Long-lived assets United States $ 49,132 $ 23,490 China (a) 91,676 86,866 Mexico 64,176 62,510 Germany 36,232 1,082 Philippines 30,734 31,129 Other countries 65,255 45,500 Total long-lived assets $ 337,205 $ 250,577 For the Three Months Ended (in thousands ) March 31, 2018 April 1, 2017 Additions to long-lived assets United States $ 2,909 $ 332 China (a) 5,144 2,392 Mexico 3,310 6,978 Germany 3,038 45 Philippines 2,162 855 Other countries 1,346 1,775 Total additions to long-lived assets $ 17,909 $ 12,377

Note 1 - Summary of Significa31

Note 1 - Summary of Significant Accounting Policies and Other Information (Details Textual) - Accounting Standards Update 2016-01 [Member] $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Cumulative Effect on Retained Earnings, Net of Tax, Total	$ 9.8
Equity Securities, FV-NI, Unrealized Gain (Loss), Total	$ 1.9

Note 1 - Summary of Significa32

Note 1 - Summary of Significant Accounting Policies and Other Information - Revenue Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Revenue	$ 417,813	$ 285,441
Electronics - Passive Products and Sensors [Member]
Revenue	114,495
Electronics - Semiconductor [Member]
Revenue	149,916
Passenger Car Products [Member]
Revenue	63,580
Automotive Sensors [Member]
Revenue	31,323
Commercial Vehicle Products [Member]
Revenue	31,228
Industrial Products [Member]
Revenue	27,271
Electronics [Member]
Revenue	264,411	153,767
Electronics [Member] | Electronics - Passive Products and Sensors [Member]
Revenue	114,495
Electronics [Member] | Electronics - Semiconductor [Member]
Revenue	149,916
Electronics [Member] | Passenger Car Products [Member]
Revenue
Electronics [Member] | Automotive Sensors [Member]
Revenue
Electronics [Member] | Commercial Vehicle Products [Member]
Revenue
Electronics [Member] | Industrial Products [Member]
Revenue
Automotive [Member]
Revenue	126,131	107,839
Automotive [Member] | Electronics - Passive Products and Sensors [Member]
Revenue
Automotive [Member] | Electronics - Semiconductor [Member]
Revenue
Automotive [Member] | Passenger Car Products [Member]
Revenue	63,580
Automotive [Member] | Automotive Sensors [Member]
Revenue	31,323
Automotive [Member] | Commercial Vehicle Products [Member]
Revenue	31,228
Automotive [Member] | Industrial Products [Member]
Revenue
Industrial [Member]
Revenue	27,271	$ 23,835
Industrial [Member] | Electronics - Passive Products and Sensors [Member]
Revenue
Industrial [Member] | Electronics - Semiconductor [Member]
Revenue
Industrial [Member] | Passenger Car Products [Member]
Revenue
Industrial [Member] | Automotive Sensors [Member]
Revenue
Industrial [Member] | Commercial Vehicle Products [Member]
Revenue
Industrial [Member] | Industrial Products [Member]
Revenue	$ 27,271

Note 2 - Acquisitions (Details

Note 2 - Acquisitions (Details Textual) $ / shares in Units, $ in Thousands	Jan. 17, 2018USD ($)$ / shares	Jul. 07, 2017USD ($)	Mar. 01, 2017USD ($)	Feb. 28, 2017USD ($)	Apr. 30, 2018USD ($)	Mar. 31, 2018USD ($)$ / shares	Mar. 31, 2018USD ($)$ / shares	Apr. 01, 2017USD ($)	Dec. 30, 2017$ / shares	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Common Stock, Par or Stated Value Per Share | $ / shares						$ 0.01	$ 0.01		$ 0.01
Share Price | $ / shares	$ 207.50
Inventory Charge Related to Step-up in Cost Basis							$ 17,896
Payments to Acquire Businesses, Net of Cash Acquired, Total							$ 306,487	$ 14,172
Finite-Lived Intangible Asset, Useful Life
Inventory, Amortization Period							150 days
Order or Production Backlog [Member]
Finite-Lived Intangible Asset, Useful Life							1 year
Monolith [Member]
Cost Method Investments										$ 3,500	$ 3,500
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners											12.00%
IXYS Corporation [Member]
Business Acquisition, Share Price | $ / shares	$ 23
Business Acquisition, Share Exchange Ratio	0.1265
Business Combination, Consideration Transferred, Excluding Value of Stock Options Converted	$ 814,800
Payments to Acquire Businesses, Gross	380,500
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	434,192
Business Combination, Value of Stock Options Converted to Company’s Stock Options	41,700
Business Combination, Consideration Transferred, Total	856,500
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables	49,100
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual						$ 86,300
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual						$ (17,800)
Business Combination, Step Up of Inventory at Acquisition Date	36,900
Inventory Charge Related to Step-up in Cost Basis							$ 17,900
Business Combination, Acquisition Related Costs							38,600
Payments to Acquire Businesses, Net of Cash Acquired, Total	302,865
IXYS Corporation [Member] | Selling, General and Administrative Expenses [Member]
Business Combination, Acquisition Related Costs							10,200
IXYS Corporation [Member] | Employee Stock Option [Member]
Allocated Share-based Compensation Expense, Total	$ 4,500						$ 5,900
U.S. Sensor [Member]
Payments to Acquire Businesses, Gross		$ 24,340
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables		1,500
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Inventory		$ 1,600
Monolith [Member]
Business Combination, Consideration Transferred, Total				$ 15,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables				$ 700
Business Acquisition, Percentage of Voting Interests Acquired				62.00%
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low				$ 500
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High				5,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value			$ 3,500	3,500
Payments to Acquire Businesses, Net of Cash Acquired, Total			14,172	14,200
Business Combination, Consideration Transferred, Commitment to Purchase Noncontrolling Interest			9,000	9,000
Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination, Total			$ 26,672	$ 26,700
Monolith [Member] | Subsequent Event [Member]
Business Combination, Consideration Transferred, Total					$ 5,000
Business Acquisition, Percentage of Voting Interests Acquired					19.00%
Business Combination, Step Acquisition, Remaining Interest Percentage					19.00%
IXYS Corporation [Member]
Number of Customers	3,500
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.01

Note 2 - Acquisitions - Prelimi

Note 2 - Acquisitions - Preliminary Price Allocation (Details) - USD ($) $ in Thousands	Jan. 17, 2018	Jul. 07, 2017	Mar. 01, 2017	Feb. 28, 2017	Mar. 31, 2018	Apr. 01, 2017	Dec. 30, 2017
Cash, net of cash acquired					$ 306,487	$ 14,172
Goodwill					840,574		$ 453,414
Goodwill					840,574		$ 453,414
Cash, net of cash acquired					$ 306,487	$ 14,172
IXYS Corporation [Member]
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
Current assets, net	154,254
Property, plant, and equipment	76,580
Intangible assets	211,600
Goodwill	381,599
Other non-current assets	31,570
Other non-current liabilities	(76,815)
	778,788
Cash	380,500
Current assets, net	154,254
Intangible assets, other than goodwill	211,600
Goodwill	381,599
	778,788
Cash, net of cash acquired	302,865
Property, plant, and equipment	$ 76,580
U.S. Sensor [Member]
Current assets, net		$ 4,635
Goodwill		16,075
		24,340
Cash		24,340
Current assets, net		4,635
Goodwill		16,075
Current liabilities		(540)
		24,340
U.S. Sensor [Member] | Patented and Unpatented Technologies [Member]
Intangible assets		1,090
Intangible assets, other than goodwill		1,090
U.S. Sensor [Member] | Trademarks and Trade Names [Member]
Intangible assets		200
Intangible assets, other than goodwill		200
U.S. Sensor [Member] | Noncompete Agreements [Member]
Intangible assets		50
Intangible assets, other than goodwill		50
U.S. Sensor [Member] | Customer Relationships [Member]
Intangible assets		2,830
Intangible assets, other than goodwill		$ 2,830
Monolith [Member]
Cash, net of cash acquired			$ 14,172	$ 14,200
Current assets, net			891
Property, plant, and equipment			789
Goodwill			20,641
Other non-current liabilities			(1,870)
Current assets, net			891
Goodwill			20,641
Current liabilities			(639)
Original investment			3,500	3,500
Cash, net of cash acquired			14,172	14,200
Non-cash, fair value of commitment to purchase non-controlling interest			9,000	9,000
Total purchase consideration			26,672	$ 26,700
Property, plant, and equipment			789
			26,672
Monolith [Member] | Patented and Unpatented Technologies [Member]
Intangible assets			6,720
Intangible assets, other than goodwill			6,720
Monolith [Member] | Noncompete Agreements [Member]
Intangible assets			140
Intangible assets, other than goodwill			$ 140

Note 2 - Acquisitions - Busines

Note 2 - Acquisitions - Business Acquisition Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Net sales	$ 434,526	$ 368,813
Income before income taxes	81,924	11,021
Net income	$ 63,933	$ 17,462
Net income per share — basic (in dollars per share)	$ 2.57	$ 0.70
Net income per share — diluted (in dollars per share)	$ 2.53	$ 0.69

Note 2 - Acquisition - Pro Form

Note 2 - Acquisition - Pro Forma Information Adjustments (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Apr. 01, 2017
Net income		$ 63,933	$ 17,462
Adjustment to Amortization [Member]
Net income	[1]	1,902	(6,276)
Adjustment to Depreciation [Member]
Net income			(94)
Acquisition-related Costs [Member]
Net income	[2]	9,976	(9,976)
Amortization of Inventory Step Up [Member]
Net income	[3]	17,896	(22,156)
Adjustment to Stock Compensation [Member]
Net income	[4]	4,479	(5,013)
Adjustment to Interest Expense [Member]
Net income	[5]		(2,582)
Adjustment to Income Tax [Member]
Net income		$ (7,701)	$ 15,374
[1]	The amortization adjustment for the three months ended March 31, 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 will be fully amortized in the fiscal 2017 pro forma results. The amortization adjustment for the three months ended April 1, 2017 reflects incremental amortization resulting for the measurement of intangibles at their fair values.
[2]	The transaction cost adjustments reflect the reversal of certain bank and attorney fees from the three months ended March 31, 2018 and recognition of those fees during the three months ended April 1, 2017.
[3]	The amortization of inventory step-up adjustment reflects the reversal of the amount recognized during the three months ended March 31, 2018 and the recognition of a full quarter of the amortization during the three months end April 1, 2017. The inventory step-up is being amortized over five months as the inventory is sold.
[4]	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 three months ended March 31, 2018. The adjustment for the three months ended April 1, 2017 reflect the incremental stock compensation for the converted stock options.
[5]	The interest expense adjustment reflects incremental interest expense related to the financing of the transaction.

Note 3 - Inventories - Componen

Note 3 - Inventories - Components of Inventories (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Raw materials	$ 66,259	$ 39,030
Work in process	96,826	27,454
Finished goods	100,884	74,305
Total	$ 263,969	$ 140,789

Note 4 - Goodwill and Other I38

Note 4 - Goodwill and Other Intangible Assets (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Finite-lived Intangible Assets Acquired	$ 211,600
Amortization of Intangible Assets, Total	11,998	$ 5,944
IXYS Corporation [Member]
Finite-lived Intangible Assets Acquired	$ 211,600

Note 4 - Goodwill and Other I39

Note 4 - Goodwill and Other Intangible Assets - Amounts for Goodwill and Changes in Carrying Value by Operating Segment (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)
Balance	$ 453,414
Additions	381,599	[1]
Currency translation	5,561
Balance	840,574
Electronics [Member]
Balance	278,959
Additions	381,599	[1]
Currency translation	2,455
Balance	663,013
Automotive [Member]
Balance	135,829
Additions		[1]
Currency translation	3,195
Balance	139,024
Industrial [Member]
Balance	38,626
Additions		[1]
Currency translation	(89)
Balance	$ 38,537
[1]	The additions resulted from the acquisition of IXYS.

Note 4 - Goodwill and Other I40

Note 4 - Goodwill and Other Intangible Assets - Details of Other Intangible Assets and Related Future Amortization Expense (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)
Finite-Lived Intangible Asset, Useful Life
Finite-lived intangible assets, gross	$ 564,947
Finite-lived intangible assets, accumulated amortization	159,541
Finite-lived intangible assets, Net Book Value	405,406
Finite-lived Intangible Assets Acquired	$ 211,600
Patents, Licenses, and Software [Member]
Finite-Lived Intangible Asset, Useful Life	10 years 219 days
Finite-lived intangible assets, gross	$ 193,622
Finite-lived intangible assets, accumulated amortization	64,012
Finite-lived intangible assets, Net Book Value	$ 129,610
Finite-lived intangible assets, useful life (Year)	8 years
Finite-lived Intangible Assets Acquired	$ 51,500
Distribution Rights [Member]
Finite-Lived Intangible Asset, Useful Life	12 years 219 days
Finite-lived intangible assets, gross	$ 44,473
Finite-lived intangible assets, accumulated amortization	33,434
Finite-lived intangible assets, Net Book Value	$ 11,039
Customer Lists, Trademarks, and Trade Names [Member]
Finite-Lived Intangible Asset, Useful Life	18 years 36 days
Finite-lived intangible assets, gross	$ 314,452
Finite-lived intangible assets, accumulated amortization	59,591
Finite-lived intangible assets, Net Book Value	$ 254,861
Finite-lived intangible assets, useful life (Year)	17 years 73 days
Finite-lived Intangible Assets Acquired	$ 147,700
Order or Production Backlog [Member]
Finite-Lived Intangible Asset, Useful Life	1 year
Finite-lived intangible assets, gross	$ 12,400
Finite-lived intangible assets, accumulated amortization	2,504
Finite-lived intangible assets, Net Book Value	$ 9,896
Finite-lived intangible assets, useful life (Year)	1 year
Finite-lived Intangible Assets Acquired	$ 12,400

Note 4 - Goodwill and Other I41

Note 4 - Goodwill and Other Intangible Assets - Estimated Amortization Expense Related to Intangible Assets with Definite Lives (Details) $ in Thousands	Mar. 31, 2018USD ($)
2,018	$ 54,938
2,019	42,005
2,020	41,747
2,021	39,928
2,022	38,918
2023 and thereafter	197,914
Total	$ 405,406

Note 5 - Debt (Details Textual)

Note 5 - Debt (Details Textual) € in Millions, $ in Millions	Jan. 16, 2018USD ($)	Oct. 13, 2017USD ($)	Mar. 04, 2016USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2020USD ($)	Dec. 30, 2017	Nov. 15, 2017USD ($)	Oct. 12, 2017USD ($)	Feb. 15, 2017USD ($)	Dec. 08, 2016USD ($)	Dec. 08, 2016EUR (€)
Euro Senior Notes, Series A and B [Member]
Debt Instrument, Face Amount | €											€ 212
Euro Senior Notes, Series A [Member]
Debt Instrument, Face Amount										$ 117
Debt Instrument, Interest Rate, Stated Percentage										1.14%	1.14%
Euro Senior Notes, Series B [Member]
Debt Instrument, Face Amount | €											€ 95
Debt Instrument, Interest Rate, Stated Percentage										1.83%	1.83%
U.S. Senior Notes, Series A and B [Member]
Debt Instrument, Face Amount										$ 125
U.S. Senior Notes, Series A [Member]
Debt Instrument, Face Amount									$ 25
Debt Instrument, Interest Rate, Stated Percentage									3.03%
U.S. Senior Notes, Series B [Member]
Debt Instrument, Face Amount									$ 100
Debt Instrument, Interest Rate, Stated Percentage									3.74%
US Senior Notes A and B Due 2025 and 2030 [Member]
Debt Instrument, Face Amount							$ 175
US Senior Notes, Series A Due 2025 [Member]
Debt Instrument, Face Amount	$ 50
Debt Instrument, Interest Rate, Stated Percentage	3.48%
US Senior Notes, Series B Due 2030 [Member]
Debt Instrument, Face Amount	$ 125
Debt Instrument, Interest Rate, Stated Percentage	3.78%
Credit Agreement [Member]
Debt Instrument, Term			5 years
Debt Agreement, Maximum Borrowing Capacity			$ 700
Line of Credit Facility, Additional Uncommitted Borrowing Capacity		$ 300	150
Line of Credit Facility, Additional Uncommitted Borrowing Capacity, Minimum Increments			$ 25
Number of Advances		2
Debt Instrument, Interest Rate, Effective Percentage				3.13%
Letters of Credit Outstanding, Amount				$ 0.1
Credit Agreement [Member] | Minimum [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.15%
Credit Agreement [Member] | Maximum [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.25%
Credit Agreement [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Debt Instrument, Basis Spread on Variable Rate			1.00%
Credit Agreement [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]
Debt Instrument, Basis Spread on Variable Rate			2.00%
Credit Agreement [Member] | Base Rate [Member] | Minimum [Member]
Debt Instrument, Basis Spread on Variable Rate			0.00%
Credit Agreement [Member] | Base Rate [Member] | Maximum [Member]
Debt Instrument, Basis Spread on Variable Rate			1.00%
Credit Agreement [Member] | Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity		$ 700	$ 575					$ 575
Line of Credit Facility, Remaining Borrowing Capacity				696.9
Credit Agreement [Member] | Term Loan Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity		200	$ 125					$ 125
Line of Credit Facility, Periodic Payment, Principal				$ 1.6
Proceeds from Issuance of Long-term Debt, Total	$ 75	$ 125
Debt Instrument, Quarterly Payments, Percentage of Loan						1.25%
Debt Instrument, Periodic Payment, Total	$ 2.5
Credit Agreement [Member] | Term Loan Credit Facility [Member] | Scenario, Forecast [Member]
Line of Credit Facility, Periodic Payment, Principal					$ 3.1

Note 5 - Debt - Carrying Amount

Note 5 - Debt - Carrying Amounts of Long-term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Unamortized debt issuance costs	$ (5,560)	$ (4,881)
Total debt	753,548	495,611
Less: Current maturities	10,111	6,250
Total long-term debt	743,437	489,361
Line of Credit [Member]
Debt, carrying amount	3,000
Unsecured Debt [Member]
Debt, carrying amount	195,000	122,500
Euro Senior Notes, Series A [Member]
Debt, carrying amount	144,041	139,623
Euro Senior Notes, Series B [Member]
Debt, carrying amount	116,956	113,369
US Senior Notes, Series A Due 2022 [Member]
Debt, carrying amount	25,000	25,000
US Senior Notes, Series B Due 2027 [Member]
Debt, carrying amount	100,000	100,000
US Senior Notes, Series A Due 2025 [Member]
Debt, carrying amount	50,000
US Senior Notes, Series B Due 2030 [Member]
Debt, carrying amount	125,000
Notes Payable, Other Payables [Member]
Debt, carrying amount	$ 111

Note 6 - Fair Value of Assets44

Note 6 - Fair Value of Assets and Liabilities (Details Textual) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Assets, Fair Value Disclosure	$ 0	$ 0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 0	$ 0

Note 6 - Fair Value of Assets45

Note 6 - Fair Value of Assets and Liabilities - Assets Measured at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments in equity securities	$ 14,754	$ 10,993
Mutual funds	9,852	7,962
Fair Value, Inputs, Level 1 [Member]
Investments in equity securities	14,754	10,993
Mutual funds	9,852	7,962
Fair Value, Inputs, Level 2 [Member]
Investments in equity securities
Mutual funds
Fair Value, Inputs, Level 3 [Member]
Investments in equity securities
Mutual funds

Note 6 - Fair Value of Assets46

Note 6 - Fair Value of Assets and Liabilities - Carrying Value and Estimated Fair Value of Senior Notes (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Euro Senior Notes, Series A [Member] | Reported Value Measurement [Member]
Senior Notes, Fair Value	$ 144,041	$ 139,623
Euro Senior Notes, Series A [Member] | Estimate of Fair Value Measurement [Member]
Senior Notes, Fair Value	142,038	138,294
Euro Senior Notes, Series B [Member] | Reported Value Measurement [Member]
Senior Notes, Fair Value	116,956	113,369
Euro Senior Notes, Series B [Member] | Estimate of Fair Value Measurement [Member]
Senior Notes, Fair Value	113,953	111,579
US Senior Notes, Series A Due 2022 [Member] | Reported Value Measurement [Member]
Senior Notes, Fair Value	25,000	25,000
US Senior Notes, Series A Due 2022 [Member] | Estimate of Fair Value Measurement [Member]
Senior Notes, Fair Value	24,301	24,737
US Senior Notes, Series B Due 2027 [Member] | Reported Value Measurement [Member]
Senior Notes, Fair Value	100,000	100,000
US Senior Notes, Series B Due 2027 [Member] | Estimate of Fair Value Measurement [Member]
Senior Notes, Fair Value	96,475	99,992
US Senior Notes, Series A Due 2025 [Member] | Reported Value Measurement [Member]
Senior Notes, Fair Value	50,000
US Senior Notes, Series A Due 2025 [Member] | Estimate of Fair Value Measurement [Member]
Senior Notes, Fair Value	48,081
US Senior Notes, Series B Due 2030 [Member] | Reported Value Measurement [Member]
Senior Notes, Fair Value	125,000
US Senior Notes, Series B Due 2030 [Member] | Estimate of Fair Value Measurement [Member]
Senior Notes, Fair Value	$ 118,303

Note 7 - Benefit Plans (Details

Note 7 - Benefit Plans (Details Textual) $ in Millions	Mar. 31, 2018USD ($)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	$ 2.3

Note 7 - Benefit Plans - Benefi

Note 7 - Benefit Plans - Benefit Plan Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Components of net periodic benefit cost:
Service cost	$ 533	$ 408
Interest cost	501	360
Expected return on plan assets	(540)	(476)
Amortization, net	74	84
Net periodic benefit cost	$ 568	$ 376

Note 8 - Shareholders' Equity49

Note 8 - Shareholders' Equity (Details Textual) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 30, 2017
Accumulated Other Comprehensive Income (Loss), Pension and Other Post-retirement Benefit Plans, Liability Adjustment Tax	$ 0.2	$ 1.4
Accounting Standards Update 2016-01 [Member]
Cumulative Effect on Retained Earnings, Net of Tax, Total	$ 9.8
IXYS Corporation [Member]
Stock Issued During Period, Shares, Acquisitions	2,092,491

Note 8 - Shareholders' Equity -

Note 8 - Shareholders' Equity - Changes in Shareholders' Equity (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Apr. 01, 2017
Balance		$ 927,556
Net income		36,029	$ 38,891
Other comprehensive income		(279)
Stock-based compensation		8,714
Withheld shares on restricted share units for withholding taxes		(2,758)
Stock options exercised		9,609
Issuance of common stock(a)	[1]	472,301
Cash dividends paid ($0.37 per share)		(9,198)
Balance		1,441,974
Parent [Member]
Balance		927,419
Net income		36,029
Other comprehensive income		(279)
Stock-based compensation		8,714
Withheld shares on restricted share units for withholding taxes		(2,758)
Stock options exercised		9,609
Issuance of common stock(a)	[1]	472,301
Cash dividends paid ($0.37 per share)		(9,198)
Balance		1,441,837
Noncontrolling Interest [Member]
Balance		137
Net income
Other comprehensive income
Stock-based compensation
Withheld shares on restricted share units for withholding taxes
Stock options exercised
Issuance of common stock(a)	[1]
Cash dividends paid ($0.37 per share)
Balance		$ 137
[1]	The issuance of common stock (2,092,491 shares) during the three months ended March 31, 2018 relates to the acquisition of IXYS. See Note 2, Acquisitions for further discussion.

Note 8 - Shareholders' Equity51

Note 8 - Shareholders' Equity - Changes in Shareholders' Equity (Details) (Parentheticals)	3 Months Ended
	Mar. 31, 2018$ / shares
Cash dividends paid, per share (in dollars per share)	$ 0.37
Parent [Member]
Cash dividends paid, per share (in dollars per share)
Noncontrolling Interest [Member]
Cash dividends paid, per share (in dollars per share)

Note 8 - Shareholders' Equity52

Note 8 - Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Dec. 30, 2017
Balance		$ 1,441,974	$ 927,556
Activity in the period		(279)
Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest [Member]
Balance	[1]	(10,839)	(10,836)
Cumulative effect adjustment (b)	[1],[2]
Activity in the period	[1]	(3)
Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Balance			9,795
Cumulative effect adjustment (b)	[1],[2]	(9,795)
Activity in the period
Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest [Member]
Balance		(62,903)	(62,627)
Cumulative effect adjustment (b)	[1],[2]
Activity in the period		(276)
AOCI Including Portion Attributable to Noncontrolling Interest [Member]
Balance		(73,742)	$ (63,668)
Cumulative effect adjustment (b)	[1],[2]	(9,795)
Activity in the period		$ (279)
[1]	The balances at March 31, 2018 and December 30, 2017 are net of taxes of $0.2 million and $1.4 million, respectively.
[2]	The Company adopted ASU 2016-01 on December 31, 2018 on a modified retrospective basis, recognizing the cumulative effect as a $9.8 million increase to retained earnings. See Note 1, Summary of Significant Accounting Policies and Other Information, for further discussion.

Note 9 - Income Taxes (Details

Note 9 - Income Taxes (Details Textual) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2018	Dec. 30, 2017	Apr. 01, 2017	Dec. 29, 2018	Dec. 30, 2017
Effective Income Tax Rate Reconciliation, Percent, Total	19.30%		18.00%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					35.00%
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability		$ 47
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability, Toll Charge		49
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability, Other Than Toll Charge		$ (2)
Deferred Tax Liabilities, Undistributed Foreign Earnings	$ 12
Foreign Tax Authority [Member]
Deferred Tax Liabilities, Undistributed Foreign Earnings	11.8
Domestic Tax Authority [Member]
Deferred Tax Liabilities, Undistributed Foreign Earnings	0.2
IXYS Corporation [Member]
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability, Toll Charge	$ 10
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				21.00%

Note 10 - Earnings Per Share (D

Note 10 - Earnings Per Share (Details Textual) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	0

Note 10 - Earnings Per Share -

Note 10 - Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Net income	$ 36,029	$ 38,891
Basic (in shares)	24,339	22,748
Effect of dilutive securities (in shares)	436	241
Diluted (in shares)	24,775	22,989
Basic earnings per share (in dollars per share)	$ 1.48	$ 1.71
Diluted earnings per share (in dollars per share)	$ 1.45	$ 1.69

Note 11 - Related Party Trans56

Note 11 - Related Party Transactions (Details Textual) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Powersem [Member]
Revenue from Related Parties	$ 0.1
Related Party Transaction, Purchases from Related Party	1.1
Accounts Receivable, Related Parties	0.1
Accounts Payable, Related Parties	0.3
EB Tech [Member]
Related Party Transaction, Amounts of Transaction	0.1
ATEC [Member]
Accounts Payable, Related Parties	0.8
Related Party Transaction, Amounts of Transaction	$ 2.4
Powersem [Member]
Equity Method Investment, Ownership Percentage	45.00%
EB Tech [Member]
Equity Method Investment, Ownership Percentage	20.00%
ATEC [Member]
Equity Method Investment, Ownership Percentage	24.00%

Note 12 - Segment Information57

Note 12 - Segment Information (Details Textual) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)	Apr. 01, 2017USD ($)
Number of Operating Segments	3
Inventory Charge Related to Step-up in Cost Basis	$ 17,896
IXYS Corporation [Member]
Business Combination, Acquisition Related Costs	38,600
Inventory Charge Related to Step-up in Cost Basis	17,900
Selling, General and Administrative Expenses [Member] | IXYS Corporation [Member]
Business Combination, Acquisition Related Costs	10,200
Other Segments [Member]
Restructuring Charges, Total	800
Other Segments [Member] | IXYS Corporation [Member]
Inventory Charge Related to Step-up in Cost Basis	17,900
Other Segments [Member] | Operating Income (Loss) [Member]
Business Combination, Acquisition Related Costs	39,500
Other Segments [Member] | Cost of Sales [Member]
Restructuring Charges, Total	500
Other Segments [Member] | Cost of Sales [Member] | IXYS Corporation [Member]
Business Combination, Acquisition Related Costs	18,400
Other Segments [Member] | Selling, General and Administrative Expenses [Member]
Business Combination, Acquisition Related Costs		$ 1,500
Restructuring Charges, Total	300
Other Segments [Member] | Selling, General and Administrative Expenses [Member] | IXYS Corporation [Member]
Business Combination, Acquisition Related Costs	16,100
Other Segments [Member] | Selling, General and Administrative Expenses [Member] | All 2017 Acquisitions [Member]
Business Combination, Acquisition Related Costs	100
Other Segments [Member] | Research and Development Expense [Member] | IXYS Corporation [Member]
Business Combination, Acquisition Related Costs	1,600
Other Segments [Member] | Backlog Amortization Expense [Member] | IXYS Corporation [Member]
Business Combination, Acquisition Related Costs	$ 2,500

Note 12 - Segment Information -

Note 12 - Segment Information - Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Apr. 01, 2017
Revenue		$ 417,813	$ 285,441
Depreciation and amortization		23,612	15,072
Operating income		37,571	48,852
Interest expense		5,423	3,120
Foreign exchange loss (gain)		(10,555)	(1,557)
Other income, net		(1,943)	(139)
Income before income taxes		44,646	47,428
Electronics [Member]
Revenue		264,411	153,767
Depreciation and amortization		13,678	8,387
Operating income		53,964	35,206
Automotive [Member]
Revenue		126,131	107,839
Depreciation and amortization		5,970	5,371
Operating income		18,390	15,065
Industrial [Member]
Revenue		27,271	23,835
Depreciation and amortization		1,460	1,314
Operating income		4,709	106
Other Segments [Member]
Depreciation and amortization		2,504
Operating income	[1]	$ (39,492)	$ (1,525)
[1]	For the first quarter of 2018, "Other" Operating income (loss) of $39.5 million consists of $38.6 million in acquisition and integration costs associated with the Company's 2018 acquisition of IXYS ($18.4 million included in Cost of sales ("COS"), of which $17.9 million relates to fair value inventory adjustments, $16.1 million included in Selling, general, and administrative expenses ("SG&A), $1.6 million in Research and development ("R&D") $2.5 million in backlog amortization expense), $0.8 million in restructuring costs ($0.5 million included in COS and $0.3 million in SG&A) and $0.1 million in year acquisition and integration costs associated with the Company's 2017 acquisitions in SG&A.

Note 12 - Segment Information59

Note 12 - Segment Information - Revenues and Long-lived Assets by Geographical Area (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Apr. 01, 2017	Dec. 30, 2017
Net sales		$ 417,813	$ 285,441
Long-lived assets		337,205		$ 250,577
Additions to long-lived assets		17,909	12,377
UNITED STATES
Net sales		123,877	86,658
Long-lived assets		49,132		23,490
Additions to long-lived assets		2,909	332
CHINA
Net sales	[1]	106,508	78,219
Long-lived assets		91,676		86,866
Additions to long-lived assets		5,144	2,392
Other Countries [Member]
Net sales	[2]	187,428	120,564
Long-lived assets		65,255		45,500
Additions to long-lived assets		1,346	1,775
MEXICO
Long-lived assets		64,176		62,510
Additions to long-lived assets		3,310	6,978
GERMANY
Long-lived assets		36,232		1,082
Additions to long-lived assets		3,038	45
PHILIPPINES
Long-lived assets		30,734		$ 31,129
Additions to long-lived assets		$ 2,162	$ 855
[1]	Includes mainland China, Taiwan, and Hong Kong.
[2]	Each country included in Other countries are less than 10% of net sales.