The exchange ratio for exchanging acquiree's common stock to acquior's common stock in a business acquisition.

No definition available.

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The fair value as of the acquisition-date of the commitment to purchase noncontrolling interest in the acquiree in a business combination.

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No definition available.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer, but excluding the value of stock options converted.

+ References

No definition available.

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Represents the value of stock options converted to company’s stock options in a business acquisition.

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No definition available.

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The amortization period for inventory, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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No definition available.

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The aggregate expense charged against earnings to allocate the cost of inventory previously stepped-up in cost basis in a business acquisition.

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No definition available.

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The number of customers that a company has.

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Tax Cuts and Jobs Act of 2017, Income Tax Expense (Benefit)

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No definition available.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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The amount of goodwill arising from a business combination that is expected to be deductible for tax purposes.

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Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination.

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No definition available.

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This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of equity interests of the acquirer, including instruments or interests issued or issuable in consideration for the business combination.

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Fair value at acquisition-date of the assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interests issued by the acquirer, including but not limited to, instruments or interests issued or issuable in consideration for the business combination.

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This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

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This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

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This element represents the amount of any measurement period adjustment (as defined) realized during the reporting period to inventory acquired in connection with a business combination for which the initial accounting was incomplete.

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Amount due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Fair value at acquisition-date of the equity interest in the acquiree held by the acquirer, immediately before the acquisition date for businesses combined in stages.

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Face amount or stated value per share of common stock.

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Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments.

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No definition available.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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Amount of gain (loss) from sale and disposal of integrated set of activities and assets capable of being conducted and managed for purpose of providing return in form of dividend, lower cost, or other economic benefit to investor, owner, member and participant.

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Gross reductions to the investment in and advance to the affiliate.

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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No definition available.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase.

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Price of a single share of a number of saleable stocks of a company.

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No definition available.

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Acquisitions and Dispositions - Narrative (Details) $ / shares in Units, $ in Thousands									1 Months Ended	3 Months Ended								12 Months Ended
	Oct. 05, 2018 USD ($)	Jan. 17, 2018 USD ($) customer $ / shares	Jul. 07, 2017 USD ($)	Mar. 01, 2017 USD ($)	Feb. 28, 2017 USD ($)	Aug. 29, 2016 USD ($)	Apr. 04, 2016 USD ($)	Mar. 25, 2016 USD ($)	Apr. 30, 2018 USD ($)	Dec. 29, 2018 USD ($) $ / shares	Sep. 29, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 30, 2017 USD ($) $ / shares	Sep. 30, 2017 USD ($)	Jul. 01, 2017 USD ($)	Apr. 01, 2017 USD ($)	Dec. 29, 2018 USD ($) $ / shares	Jan. 17, 2018 USD ($) $ / shares	Dec. 30, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Common stock, par value (in dollars per share) \| $ / shares										$ 0.01				$ 0.01				$ 0.01		$ 0.01
Share price (in dollars per share) \| $ / shares		$ 207.50																	$ 207.50
TCJA one-time charge										$ 3,200				$ 49,000
Allocated share based compensation																		$ 28,200		$ 17,300	$ 12,800
Non-cash inventory charges																		36,927		1,607	7,834
Acquisition related costs										3,200	$ 2,900	$ 2,400	$ 11,700	$ 1,400	$ 4,800	$ 300	$ 1,500
Cost method investments										7,900								7,900
Cash, net of cash acquired																		$ 318,474		38,512	471,118
Inventory amortization period																		5 months
Additions																		$ 382,903		36,716
Order backlog
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)																		12 months
PolySwitch
Business Acquisition [Line Items]
Consideration transferred								$ 348,300
Revenue of acquiree since acquisition																				126,500
Inventory adjustment								$ 6,900
Voting interest acquired								100.00%
Total purchase consideration								$ 348,292
Expected tax deductible amount								$ 64,900
PolySwitch \| Customer relationships
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)								15 years
PolySwitch \| Patented and unpatented technologies
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)								10 years
IXYS Corporation
Business Acquisition [Line Items]
Share price (in dollars per share) \| $ / shares		$ 23																	$ 23
Share exchange ratio		0.1265																	0.1265
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
Reduction in certain investments										2,600
Revenue of acquiree since acquisition																		$ 378,200
Earnings (loss) of acquiree since acquisition																		22,200
Acquisition related costs																		11,000
Cash, net of cash acquired		302,865
Total purchase consideration		$ 778,788
U.S. Sensor
Business Acquisition [Line Items]
Cash			$ 24,340
Receivables			1,500
Inventory adjustment			$ 1,600
Monolith
Business Acquisition [Line Items]
Consideration transferred	$ 5,000				$ 15,000								$ 5,000
Receivables				$ 700
Cost method investments																					3,500	$ 3,500
Ownership percentage by noncontrolling owners																						12.00%
Voting interest acquired	19.00%				62.00%								19.00%
Original investment				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
Monolith \| Stockholders of Monolith
Business Acquisition [Line Items]
Consideration transferred									$ 49,100				$ 4,000
ON Portfolio
Business Acquisition [Line Items]
Cash						$ 104,000
Consideration transferred						104,000
Revenue of acquiree since acquisition																				21,800
Inventory adjustment						700
Expected tax deductible amount						$ 7,300
ON Portfolio \| Customer relationships
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)						13 years 182 days
ON Portfolio \| Non-compete agreement
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)						4 years
Menber's S.p.A.
Business Acquisition [Line Items]
Consideration transferred							$ 19,200
Revenue of acquiree since acquisition																				17,300
Inventory adjustment							200
Cash, net of cash acquired							$ 19,162
Menber's S.p.A. \| Customer relationships
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)							10 years
Menber's S.p.A. \| Patented and unpatented technologies
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)							5 years
Menber's S.p.A. \| Trademarks and tradenames
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)							10 years
Other \| Selling, General and Administrative Expenses
Business Acquisition [Line Items]
Acquisition related costs																				8,000	$ 29,200
Other \| Operating Income (Loss)
Business Acquisition [Line Items]
Acquisition related costs																		88,700
Inventory adjustment																		36,900
Electronics
Business Acquisition [Line Items]
Additions								$ 103,800										382,903		36,716
Automotive
Business Acquisition [Line Items]
Additions								$ 61,300										$ 0		0
Marine Product Line
Business Acquisition [Line Items]
Loss on disposition of business																				$ 1,400
IXYS Corporation
Business Acquisition [Line Items]
Number of customers \| customer		3,500
Common stock, par value (in dollars per share) \| $ / shares		$ 0.01																	$ 0.01
Minimum \| Trademarks and tradenames
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)																		5 years
Minimum \| ON Portfolio \| Patented and unpatented technologies
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)						6 years
Maximum \| Trademarks and tradenames
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)																		20 years
Maximum \| ON Portfolio \| Patented and unpatented technologies
Business Acquisition [Line Items]
Weighted Average Useful Life (Years)						8 years 182 days
Toll Charge
Business Acquisition [Line Items]
TCJA one-time charge										2,300
Toll Charge \| IXYS Corporation
Business Acquisition [Line Items]
TCJA one-time charge		$ 7,000								$ (1,000)	$ (2,000)								$ 7,000
Options \| IXYS Corporation
Business Acquisition [Line Items]
Allocated share based compensation																		$ 11,900
Options \| IXYS Corporation \| Selling, General and Administrative Expenses
Business Acquisition [Line Items]
Allocated share based compensation																		$ 4,500