Vicor (VICR) 10-K 9 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 28, 2018	Jun. 30, 2017
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	VICR
Entity Registrant Name	VICOR CORP
Entity Central Index Key	751,978
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 301,433,000
Class A Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		27,748,045
Class B Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		11,758,218

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 44,230	$ 56,170
Accounts receivable, less allowance of $159 in 2017 and $153 in 2016	34,487	25,216
Inventories, net	36,499	27,136
Other current assets	3,616	3,250
Total current assets	118,832	111,772
Long-term deferred tax assets	210	38
Long-term investments, net	2,525	2,508
Property, plant and equipment, net	41,356	37,574
Other assets	2,801	2,175
Total assets	165,724	154,067
Current liabilities:
Accounts payable	9,065	7,588
Accrued compensation and benefits	9,891	8,965
Accrued expenses	2,989	2,179
Income taxes payable	300	92
Deferred revenue	5,791	3,403
Total current liabilities	28,036	22,227
Long-term deferred revenue	303	374
Contingent consideration obligations	678	253
Long-term income taxes payable	195	196
Other long-term liabilities	93
Total liabilities	29,305	23,050
Commitments and contingencies (Note 15)
Vicor Corporation stockholders' equity:
Preferred Stock, $.01 par value, 1,000,000 shares authorized; no shares issued
Additional paid-in capital	181,395	176,344
Retained earnings	93,605	93,438
Accumulated other comprehensive loss	(478)	(561)
Treasury stock at cost: 11,671,486 shares in 2017 and 2016	(138,927)	(138,927)
Total Vicor Corporation stockholders' equity	136,114	130,809
Noncontrolling interest	305	208
Total equity	136,419	131,017
Total liabilities and equity	165,724	154,067
Class B Common Stock [Member]
Vicor Corporation stockholders' equity:
Common Stock	118	118
Total equity	118	118
Common Stock [Member]
Vicor Corporation stockholders' equity:
Common Stock	$ 401	$ 397

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) $ in Thousands	Dec. 31, 2017USD ($)Vote$ / sharesshares	Dec. 31, 2016USD ($)Vote$ / sharesshares
Accounts receivable, allowance | $	$ 159	$ 153
Preferred Stock, par value | $ / shares	$ 0.01	$ 0.01
Preferred Stock, shares authorized	1,000,000	1,000,000
Preferred Stock, shares issued	0	0
Treasury stock, shares	11,671,486	11,671,486
Class B Common Stock [Member]
Common Stock, votes per share | Vote	10	10
Common Stock, par value | $ / shares	$ 0.01	$ 0.01
Common Stock, shares authorized	14,000,000	14,000,000
Common Stock, shares issued	11,758,218	11,758,218
Common Stock, shares outstanding	11,758,218	11,758,218
Common Stock [Member]
Common Stock, votes per share | Vote	1	1
Common Stock, par value | $ / shares	$ 0.01	$ 0.01
Common Stock, shares authorized	62,000,000	62,000,000
Common Stock, shares issued	39,324,029	38,922,489
Common Stock, shares outstanding	27,652,543	27,251,003

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net revenues	$ 227,830	$ 200,280	$ 220,194
Cost of revenues	126,174	109,071	120,676
Gross margin	101,656	91,209	99,518
Operating expenses:
Selling, general and administrative	58,092	55,675	58,313
Research and development	44,924	41,848	41,472
Total operating expenses	103,016	97,523	99,785
Loss from operations	(1,360)	(6,314)	(267)
Other income (expense), net:
Total unrealized gains (losses) on available-for-sale securities, net	17	(18)	(49)
Portion of (losses) gains recognized in other comprehensive income (loss)	(6)	31	61
Net credit gains recognized in earnings	11	13	12
Other income (expense), net	1,251	271	13
Total other income (expense), net	1,262	284	25
Loss before income taxes	(98)	(6,030)	(242)
Less: (Benefit) provision for income taxes	(356)	231	(401)
Gain from sale of equity method investment, net of tax			5,000
Consolidated net income (loss)	258	(6,261)	5,159
Less: Net income (loss) attributable to noncontrolling interest	91	(14)	232
Net income (loss) attributable to Vicor Corporation	$ 167	$ (6,247)	$ 4,927
Net income (loss) per common share attributable to Vicor Corporation:
Basic	$ 0	$ (0.16)	$ 0.13
Diluted	$ 0	$ (0.16)	$ 0.13
Shares used to compute net income (loss) per common share attributable to Vicor Corporation:
Basic	39,228	38,842	38,754
Diluted	39,933	38,842	39,146

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Consolidated net income (loss)		$ 258	$ (6,261)	$ 5,159
Foreign currency translation gains (losses), net of tax benefit	[1]	83	52	(52)
Unrealized gains (losses) on available-for-sale securities, net of tax	[1]	6	(31)	(59)
Other comprehensive income (loss)		89	21	(111)
Consolidated comprehensive income (loss)		347	(6,240)	5,048
Less: Comprehensive income (loss) attributable to noncontrolling interest		97	(9)	227
Comprehensive income (loss) attributable to Vicor Corporation		$ 250	$ (6,231)	$ 4,821
[1]	The deferred tax assets associated with cumulative foreign currency translation gains (losses) and cumulative unrealized gains (losses) on available for sale securities are completely offset by a tax valuation allowance as of December 31, 2017, 2016, and 2015. Therefore, there is no income tax benefit (provision) recognized for the three years ended December 31, 2017.

Consolidated Statements of Com6

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Recognized income tax benefit (provision)	$ 0	$ 0	$ 0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Consolidated net income (loss)	$ 258	$ (6,261)	$ 5,159
Adjustments to reconcile consolidated net income (loss) to net cash (used for) provided by operating activities:
Depreciation and amortization	8,893	8,438	9,142
Stock-based compensation expense	1,735	506	1,782
Increase in refundable income taxes	(736)
Increase in contingent consideration obligations	650
(Decrease) increase in long-term income taxes payable	(1)	4	(675)
Deferred income taxes	(172)	(78)	(183)
Decrease in long-term deferred revenue	(71)	(94)	(139)
Increase in other long-term liabilities	93
(Gain) loss on disposal of equipment	(14)	4	(60)
Provision (benefit) for doubtful accounts	6	(22)	(18)
Credit gain on available-for-sale securities	(11)	(13)	(12)
Gain from sale of equity method investment			(5,000)
Increase in other assets		(505)
Gain from disposition of consolidated subsidiary			(28)
Change in current assets and liabilities, net	(13,094)	(1,435)	1,499
Net cash (used for) provided by operating activities	(2,464)	544	11,467
Investing activities:
Additions to property, plant and equipment	(12,545)	(8,428)	(9,090)
Proceeds from sale of equipment	14	2	60
Increase (decrease) in other assets	5	(93)	(204)
Sales and maturities of investments			360
Proceeds from sale of equity method investment			5,000
Deconsolidation of subsidiary			(392)
Net cash used for investing activities	(12,526)	(8,519)	(4,266)
Financing activities:
Proceeds from issuance of Common Stock	3,300	1,584	820
Payment of contingent consideration obligations	(225)	(99)
Deconsolidation of subsidiary		(372)
Acquisition of noncontrolling interest			(216)
Net cash provided by financing activities	3,075	1,113	604
Effect of foreign exchange rates on cash	(25)	52	(12)
Net (decrease) increase in cash and cash equivalents	(11,940)	(6,810)	7,793
Cash and cash equivalents at beginning of year	56,170	62,980	55,187
Cash and cash equivalents at end of year	44,230	56,170	62,980
Change in current assets and liabilities, excluding effects of disposition of consolidated subsidiary:
Accounts receivable	(9,210)	780	2,201
Inventories, net	(9,309)	(3,677)	1,880
Other current assets	(357)	(158)	(111)
Accounts payable and accrued liabilities	3,186	339	(1,301)
Accrued severance charges		(195)	(1,709)
Income taxes payable	208	61	(10)
Deferred revenue	2,388	1,415	549
Change in current assets and liabilities, net	(13,094)	(1,435)	1,499
Supplemental disclosures:
Cash paid during the year for income taxes, net of refunds	$ 373	$ 230	$ 675

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Total Vicor Corporation Stockholders' Equity [Member]	Noncontrolling Interest [Member]	Class B Common Stock [Member]
Beginning Balance at Dec. 31, 2014	$ 130,552	$ 393	$ 171,901	$ 94,758	$ (471)	$ (138,927)	$ 127,772	$ 2,780	$ 118
Sales of Common Stock	820	2	818				820
Acquisition of noncontrolling interest	(360)		(144)				(144)	(216)
Disposition of consolidated subsidiary	(1,742)		(5)				(5)	(1,737)
Stock-based compensation expense	1,782		1,782				1,782
Net settlement stock option exercises	(22)		(22)				(22)
Other	7		7				7
Components of comprehensive income, net of tax
Net income	5,159			4,927			4,927	232
Other comprehensive income (loss)	(111)				(106)		(106)	(5)
Total comprehensive income	5,048						4,821	227
Ending Balance at Dec. 31, 2015	136,085	395	174,337	99,685	(577)	(138,927)	135,031	1,054	118
Sales of Common Stock	1,589	2	1,587				1,589
Acquisition of noncontrolling interest	(918)		(81)				(81)	(837)
Stock-based compensation expense	506		506				506
Net settlement stock option exercises	(5)		(5)				(5)
Components of comprehensive income, net of tax
Net income	(6,261)			(6,247)			(6,247)	(14)
Other comprehensive income (loss)	21				16		16	5
Total comprehensive income	(6,240)						(6,231)	(9)
Ending Balance at Dec. 31, 2016	131,017	397	176,344	93,438	(561)	(138,927)	130,809	208	118
Sales of Common Stock	3,300	4	3,296				3,300
Stock-based compensation expense	1,735		1,735				1,735
Other	20	0	20				20
Components of comprehensive income, net of tax
Net income	258			167			167	91
Other comprehensive income (loss)	89				83		83	6
Total comprehensive income	347						250	97
Ending Balance at Dec. 31, 2017	$ 136,419	$ 401	$ 181,395	$ 93,605	$ (478)	$ (138,927)	$ 136,114	$ 305	$ 118

Description of Business

Description of Business	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	1. DESCRIPTION OF BUSINESS Vicor Corporation (the “Company” or “Vicor”) designs, develops, manufactures, and markets modular power components and power systems for converting, regulating and controlling electric current. The Company also licenses certain rights to its technology in return for recurring royalties. The principal markets for the Company’s power converters and systems are large original equipment manufacturers (“OEMs”) and their contract manufacturers, and smaller, lower volume users, which are broadly distributed across several major market areas.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Significant Accounting Policies	2. SIGNIFICANT ACCOUNTING POLICIES Principles of consolidation The Consolidated Financial Statements include the accounts of the Company and its subsidiaries. All intercompany transactions and balances have been eliminated upon consolidation. One of the Company’s subsidiaries was not majority owned by the Company prior to 2016, and a second was not majority owned prior to March 31, 2016. Prior to the transactions described in Note 9, these entities were consolidated by the Company as management believed that the Company had the ability to exercise control over their activities and operations. Use of estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingencies at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Such estimates and assumptions relate to the useful lives of fixed assets and identified intangible assets, recoverability of long-lived assets, fair value of long-term investments, allowances for doubtful accounts, the net realizable value of inventory, potential reserves relating to litigation matters, accrued liabilities, accrued taxes, deferred tax valuation allowances, assumptions pertaining to share-based payments, and other reserves. Actual results could differ from those based on these estimates and assumptions, and such differences may be material to the financial statements. Revenue recognition Product revenue is recognized in the period when persuasive evidence of an arrangement with a customer exists, the products are shipped and title has transferred to the customer, the price is fixed or determinable, and collection is considered probable. The Company defers revenue and the related cost of sales on shipments to stocking distributors until the distributors resell the products to their customers. The agreements with these stocking distributors allow them to receive price adjustment credits or to return qualifying products for credit, as determined by the Company, in order to reduce the amounts of slow-moving, discontinued, or obsolete product from their inventory. These stocking distributors are also granted price adjustment credits in the event of a price decrease subsequent to the date the product was shipped and invoiced to the stocking distributor. Given the uncertainties associated with the levels of price adjustment credits to be granted to stocking distributors, the sales price to the stocking distributor is not fixed or determinable until the stocking distributor resells the products to its customers. Therefore, the Company defers revenue and the related cost of sales on shipments to stocking distributors until the stocking distributors resell the products to their customers. Accordingly, the Company’s revenue fully reflects end-customer end-customers. The Company evaluates revenue arrangements with potential multi-element deliverables to determine if there is more than one unit of accounting. A deliverable constitutes a separate unit of accounting when it has standalone value and there are no customer-negotiated refund or return rights for the undelivered elements. The Company enters into arrangements containing multiple elements that may include a combination of non-recurring License fees are recognized as earned. The Company recognizes revenue on such arrangements only when the contract is signed, the license term has begun, all obligations have been delivered to the customer, and collection is probable. Foreign currency translation The financial statements of Vicor Japan Company, Ltd. (“VJCL”), a majority-owned subsidiary, for which the functional currency is the Japanese Yen, have been translated into U.S. Dollars using the exchange rate in effect at the balance sheet date for balance sheet amounts and the average exchange rates in effect during the year for income statement amounts. The gains and losses resulting from the changes in exchange rates from year to year have been reported in other comprehensive income. Transaction gains and losses resulting from the remeasurement of foreign currency denominated assets and liabilities of the Company’s foreign subsidiaries where the functional currency is the U.S. Dollar are included in other income (expense), net. Foreign currency gains (losses) included in other income (expense), net, were approximately $323,000, $(268,000), and $(161,000) in 2017, 2016, and 2015, respectively. Cash and cash equivalents Cash and cash equivalents include funds held in disbursement (i.e., checking) and money market accounts, certificates of deposit, and debt securities with maturities of less than three months at the time of purchase. Cash and cash equivalents are valued at cost, approximating market value. The Company’s money market securities, which are classified as cash equivalents on the balance sheet, are purchased and redeemed at par value. Their estimated fair value is equal to their cost, and, due to the nature of the securities and their classification as cash equivalents, there are no unrealized gains or losses recorded at the balance sheet dates. Long-term investments The Company’s principal sources of liquidity are its existing balances of cash and cash equivalents, as well as cash generated from operations. Consistent with the guidelines of the Company’s investment policy, the Company can invest, and has historically invested, its cash balances in demand deposit accounts, money market funds, and auction rate securities meeting certain quality criteria. All of the Company’s investments are subject to credit, liquidity, market, and interest rate risk. The Company’s long-term investments are classified as available-for-sale Available-for-sale non-credit The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity, the net amount of which, along with interest and realized gains and losses, is included in “Other income (expense), net” in the Consolidated Statements of Operations. The Company periodically evaluates investments to determine if impairment is required, whether an impairment is other than temporary, and the measurement of an impairment loss. The Company considers a variety of impairment indicators such as, but not limited to, a significant deterioration in the earnings performance, credit rating, or asset quality of the investment. Fair value measurements The Company accounts for certain financial assets at fair value, defined as the price that would be received to sell an asset or paid to transfer a liability (i.e., an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. A three-level hierarchy is used to show the extent and level of judgment used to estimate fair value measurements: Level 1 Inputs used to measure fair value are unadjusted quoted prices available in active markets for the identical assets or liabilities as of the reporting date. Level 2 Inputs used to measure fair value, other than quoted prices included in Level 1, are either directly or indirectly observable as of the reporting date through correlation with market data, including quoted prices for similar assets and liabilities in active markets and quoted prices in inactive markets. Level 2 also includes assets and liabilities valued using models or other pricing methodologies that do not require significant judgment since the input assumptions used in the models, such as interest rates and volatility factors, are corroborated by readily observable data from actively quoted markets for substantially the full term of the financial instrument. Level 3 Inputs used to measure fair value are unobservable inputs supported by little or no market activity and reflect the use of significant management judgment. These values are generally determined using pricing models for which the assumptions utilize management’s estimates of market participant assumptions. The carrying amounts of cash and cash equivalents, accounts receivable and accounts payable approximate fair value because of the short maturity of these financial instruments. Allowance for doubtful accounts The Company maintains allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments, based on assessments of customers’ credit-risk profiles and payment histories. If the financial condition of the Company’s customers were to deteriorate, resulting in an impairment of their ability to make payments, additional allowances may be required. The Company does not require collateral from its customers, although there have been circumstances when the Company has required cash in advance (i.e., a partial down-payment) to facilitate orders in excess of a customer’s established credit limit. To date, such amounts have not been material. Inventories Inventories are valued at the lower of cost (determined using the first-in, first-out The Company provides reserves for inventories estimated to be excess, obsolete, or unmarketable. The Company’s estimation process for assessing net realizable value is based upon its known backlog, projected future demand, historical consumption and expected market conditions. If the Company’s estimated demand and/or market expectations were to change or if product sales were to decline, the Company’s estimation process may cause larger inventory reserves to be recorded, resulting in larger charges to cost of revenues. Concentrations of risk Financial instruments potentially subjecting the Company to significant concentrations of credit risk consist principally of cash and cash equivalents, of which a significant portion is held by one financial institution, long-term investments, and trade accounts receivable. The Company maintains cash and cash equivalents and certain other financial instruments with various large financial institutions. Generally, amounts invested with these financial institutions are in excess of federal deposit insurance limits. The Company has not experienced any losses in such accounts, and management believes the Company is not exposed to significant credit risk. The Company’s long-term investments consist of highly rated (Aaa/AA+) municipal and corporate debt securities which, as of December 31, 2017, consist of a single auction rate security with a par value of $3,000,000, which is collateralized by student loans. Through December 31, 2017, auctions held for the Company’s auction rate security have failed. The funds associated with an auction rate security that has failed auction may not be accessible until a successful auction occurs, a buyer is found outside of the auction process, the security is called, or the underlying securities have matured. If the credit rating of the issuer of the auction rate security held deteriorates, the Company may be required to adjust the carrying value of the investment for an other-than-temporary decline in value through an impairment charge. The Company’s investment policy, approved by the Board of Directors, limits the amount the Company may invest in any issuer, thereby reducing credit risk concentrations. The Company’s products are sold worldwide to customers ranging from smaller, independent manufacturers of highly specialized electronic devices, to larger OEMs and their contract manufacturers. The Company’s Brick Business Unit (“BBU”) has customers concentrated in aerospace and aviation, defense electronics, industrial automation and equipment, medical diagnostics, rail transportation, and test and measurement instrumentation. The Company’s VI Chip and Picor subsidiaries have customers concentrated in the datacenter and supercomputer segments of the computing market, although they also target applications in aerospace and aviation, defense electronics, networking equipment, solid state lighting, test and measurement instrumentation, and transportation (electric and hybrid vehicles and autonomous vehicles). While, overall, the Company has a broad customer base and sells into a variety of industries, VI Chip and Picor have derived a substantial portion of their revenue from a limited number of customers. This concentration of revenue is a reflection of the relatively early stage of adoption of the technologies, architectures and products offered by these subsidiaries, and their targeting of market leading innovators as initial customers. Concentrations of credit risk with respect to trade accounts receivable are limited due to the number of entities comprising the Company’s customer base. As of December 31, 2017 and 2016, one customer accounted for approximately 17.5% and 14.2%, respectively, of trade account receivables. Components and materials used in the Company’s products are purchased from a variety of vendors. While most of the components are available from multiple sources, some key components for certain VI Chip and Picor products, in particular, are supplied by single vendors. In instances of single source items, the Company maintains levels of inventories management considers appropriate to enable meeting the delivery requirements of customers. If suppliers or subcontractors cannot provide their products or services on time or to the required specifications, the Company may not be able to meet the demand for its products and its delivery times may be negatively affected. Long-lived assets The Company reviews property, plant and equipment and finite-lived intangible assets for impairment whenever events or changes in circumstances indicate the carrying value of such assets may not be recoverable. Management determines whether the carrying value of an asset or asset group is recoverable based on comparison to the undiscounted expected future cash flows the assets are expected to generate over their remaining economic lives. If an asset value is not recoverable, the impairment loss is equal to the amount by which the carrying value of the asset exceeds its fair value, which is determined by either a quoted market price, if any, or a value determined by utilizing a discounted cash flow technique. Evaluation of impairment of long-lived assets requires estimates of future operating results that are used in the preparation of the expected future undiscounted cash flows. Actual future operating results and the remaining economic lives of our long-lived assets could differ from the estimates used in assessing the recoverability of these assets. These differences could result in impairment charges, which could be material. Intangible assets Values assigned to patents are amortized using the straight-line method over periods ranging from three to 20 years. Patents and other intangible assets are included in “Other assets” in the accompanying Consolidated Balance Sheets. Advertising expense The cost of advertising is expensed as incurred. The Company incurred $2,150,000, $1,818,000, and $1,762,000 in advertising costs during 2017, 2016 and 2015, respectively. Product warranties The Company generally offers a two-year Legal Costs Legal costs in connection with litigation are expensed as incurred. Net income (loss) per common share The Company computes basic net income (loss) per share using the weighted average number of common shares outstanding and diluted net income (loss) per share using the weighted average number of common shares outstanding plus the effect of outstanding dilutive stock options, if any. The following table sets forth the computation of basic and diluted net income (loss) per share for the years ended December 31 (in thousands, except per share amounts): 2017 2016 2015 Numerator: Net income (loss) attributable to Vicor Corporation $ 167 $ (6,247 ) $ 4,927 Denominator: Denominator for basic net income (loss) per share-weighted average shares (1) 39,228 38,842 38,754 Effect of dilutive securities: Employee stock options (2) 705 — 392 Denominator for diluted net income (loss) per share — adjusted weighted-average shares and assumed conversions (3) 39,933 38,842 39,146 Basic net income (loss) per share $ 0.00 $ (0.16 ) $ 0.13 Diluted net income (loss) per share $ 0.00 $ (0.16 ) $ 0.13 (1) Denominator represents weighted average number of Common Shares and Class B Common Shares outstanding. (2) Options to purchase 53,913, 1,696,222 and 238,792 shares of Common Stock in 2017, 2016, and 2015, respectively, were not included in the calculation of net income (loss) per share as the effect would have been antidilutive. (3) Denominator represents weighted average number of Common Shares and Class B Common Shares outstanding for the year, adjusted to include the dilutive effect, if any, of outstanding options. Income taxes Deferred tax assets and liabilities are determined based on the differences between financial reporting and tax bases of assets and liabilities and are measured using the enacted income tax rates and laws expected to be in effect when the temporary differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance if management determines it is more likely than not that some portion or all of the deferred tax assets will not be realized. All deferred tax assets and liabilities are classified as noncurrent. The Company follows a two-step “more-likely-than-not” “more-likely-than-not” Stock-based compensation The Company uses the Black-Scholes option-pricing model to calculate the fair value of stock option awards, whether they possess time-based vesting provisions or performance-based vesting provisions, and options granted under the Company’s Employee Stock Purchase Plan, as of their grant date. For stock options with time-based vesting provisions, the calculated compensation expense, net of expected forfeitures, is recognized on a straight-line basis over the service period of the award, which is generally five years for stock options. For stock options with performance-based vesting provisions, recognition of compensation expense, net of expected forfeitures, commences if and when the achievement of the performance criteria is deemed probable. For stock options with performance-based vesting provisions, compensation expense, net of expected forfeitures, when recognized, is recognized over the relevant performance period. Comprehensive income (loss) The components of comprehensive income (loss) include, in addition to net income (loss), unrealized gains and losses on investments, net of tax and foreign currency translation adjustments related to VJCL, net of tax. Impact of recently issued accounting standards In May 2017, the Financial Accounting Standards Board (“FASB”) issued guidance about which changes to the terms or conditions of a stock-based payment award require an entity to apply modification accounting in Topic 718, Compensation — Stock Compensation In August 2016, the FASB issued guidance to clarify how certain cash receipts and cash payments should be presented in the statement of cash flows. These include debt prepayment, settlement of zero-coupon In June 2016, the FASB issued new guidance which will require measurement and recognition of expected credit losses on certain types of financial instruments. It also modifies the impairment model for available-for-sale In March 2016, the FASB issued new guidance for employee stock-based payment accounting, which makes several modifications to existing guidance related to the accounting for forfeitures, employer tax withholding on stock-based compensation and the financial statement presentation of excess tax benefits or deficiencies. This new guidance also clarifies the statement of cash flows presentation for certain components of stock-based awards. In terms of the accounting for forfeitures, the new guidance allows an option for them to either be estimated, as currently required, or recognized when they occur. The Company will continue to estimate forfeitures. The Company adopted the new standard on January 1, 2017. (See Note 14 – Income Taxes for additional details on the impact of adoption). In February 2016, the FASB issued new guidance for lease accounting, which will require lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. The new guidance establishes a right-of-use In May 2014, the FASB issued new guidance for revenue recognition, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The new guidance, which includes several amendments, replaces most of the prior revenue recognition guidance under U.S. Generally Accepted Accounting Principles (“U.S. GAAP”). The Company’s assessment of the new standard’s impact is substantially complete. The Company will adopt the new guidance as of January 1, 2018 using the modified retrospective method. The most significant impact of the adoption is on the timing of recognition of sales to its stocking distributors. Through December 31, 2017, the Company deferred revenue and the related cost of sales on shipments to stocking distributors until the distributors resold the products to their customers. Upon adoption, the Company is no longer permitted to defer revenue until sale by the stocking distributor to the end customer, but rather, is required to estimate the effects of returns and allowances provided to stocking distributors and record revenue at the time of sale to the stocking distributor. The cumulative effect of adopting this guidance, to be recognized as an increase to the balance of retained earnings as of January 1, 2018, is currently estimated to be approximately $3,300,000. The implementation team’s remaining tasks are to complete documentation for the systems and controls to support the revenue recognition and disclosure requirements under the new standard, and to complete the required disclosures in preparation for filing the Company’s Form 10-Q Other new pronouncements issued but not effective until after December 31, 2017 are not expected to have a material impact on the Company’s consolidated financial statements.

Stock-Based Compensation and Em

Stock-Based Compensation and Employee Benefit Plans	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation and Employee Benefit Plans	3. STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS Vicor currently grants options for the purchase of Common Stock (i.e., “stock options”) under the following equity compensation plan that is stockholder-approved: Amended and Restated 2000 Stock Option and Incentive Plan, as amended and restated (the “2000 Plan”) non-employee non-qualified non-employee Picor Corporation (“Picor”), a privately held, majority-owned subsidiary of Vicor, currently grants stock options under the following equity compensation plan that has been approved by its Board of Directors: Amended and Restated 2001 Stock Option and Incentive Plan (the “2001 Picor Plan”) non-employee Non-qualifying VI Chip Corporation (“VI Chip”), a privately held, majority-owned subsidiary of Vicor, currently grants stock options under the following equity compensation plan that has been approved by its Board of Directors: Amended and Restated 2007 Stock Option and Incentive Plan (the “2007 VI Chip Plan”) non-employee Non-qualifying All time-based (i.e., non-performance-based) non-performance-based) On December 31, 2010, the Company granted 2,984,250 non-qualified On April 26, 2017, the Company’s Board of Directors approved the Vicor Corporation 2017 Employee Stock Purchase Plan (the “Plan” or the “ESPP”). The ESPP became effective on June 16, 2017, the date the Company’s stockholders approved the Plan at the 2017 Annual Meeting of Stockholders. The Company has reserved 2,000,000 shares of Common Stock under the Plan for issuance to eligible employees who elect to participate. The ESPP is intended to qualify as an “employee stock purchase plan” under Section 423 of the Code. The ESPP operates in successive periods of approximately six months, each referred to as an “offering period.” Generally, offering periods commence on or around September 1 and March 1 and end on or around the following February 28 or August 31, respectively. Under the ESPP, an option is granted to participating employees on the first day of an offering period to purchase shares of the Company’s Common Stock at the end of that offering period at a purchase price equal to 85% of the lesser of the fair market value of a share of Common Stock on either the first day or the last day of that offering period. The purchase of shares is funded by means of periodic payroll deductions, which may not exceed 15.0% of the employee’s eligible compensation, as defined in the Plan. Among other provisions, the Plan limits the number of shares that can be purchased by a participant during any offering period and cumulatively for any calendar year. Stock-based compensation expense for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Cost of revenues $ 187 $ 95 $ 230 Selling, general and administrative 1,125 412 1,246 Research and development 423 (1 ) 306 Total stock-based compensation $ 1,735 $ 506 $ 1,782 The increase in stock-based compensation expense in 2017 compared to 2016, and the decrease in 2016 compared to 2015, was primarily due to the reversal of previously recorded stock-based compensation for VI Chip performance-based options in 2016, as described above. Compensation expense by type of award for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Stock options $ 1,546 $ 506 $ 1,782 ESPP 189 — — Total stock-based compensation $ 1,735 $ 506 $ 1,782 The fair value for non performance-based stock options awarded for the years shown below was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions: Vicor: 2017 2016 2015 Risk-free interest rate 2.1 % 1.5 % 2.0 % Expected dividend yield — — — Expected volatility 43 % 45 % 51 % Expected lives (years) 7.1 7.2 7.2 VI Chip: 2017 2016 2015 Risk-free interest rate 1.9 % 1.7 % 2.1 % Expected dividend yield — — — Expected volatility 32 % 34 % 37 % Expected lives (years) 6.5 6.5 6.5 Picor: 2017 2016 2015 Risk-free interest rate 1.9 % 1.5 % 1.9 % Expected dividend yield — — — Expected volatility 48 % 42 % 41 % Expected lives (years) 6.5 6.5 6.5 Risk-free interest rate: Vicor zero-coupon Picor and VI Chip Expected dividend yield: Vicor Picor and VI Chip Expected volatility: Vicor Picor VI Chip Expected term: Vicor Picor and VI Chip Forfeiture rate: The amount of stock-based compensation recognized during a period is based on the value of the portion of the awards that are ultimately expected to vest. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The term “forfeitures” is distinct from “cancellations” or “expirations” and represents only the unvested portion of the surrendered option. The forfeiture analysis is re-evaluated Vicor Picor VI Chip Vicor Stock Options A summary of the activity under the 2000 Plan as of December 31, 2017 and changes during the year then ended, is presented below (in thousands except for share and weighted-average data): Options Weighted- Weighted- Aggregate Outstanding on December 31, 2016 1,696,222 $ 8.82 Granted 96,322 $ 18.41 Forfeited and expired (25,087 ) $ 10.92 Exercised (401,540 ) $ 8.21 Outstanding on December 31, 2017 1,365,917 $ 9.63 6.21 $ 15,409 Exercisable on December 31, 2017 707,244 $ 8.01 5.82 $ 9,116 Vested or expected to vest as of December 31, 2017(1) 1,332,671 $ 9.54 6.19 $ 15,161 (1) In addition to the vested options, the Company expects a portion of the unvested options to vest at some point in the future. The number of options expected to vest is calculated by applying an estimated forfeiture rate to the unvested options. As of December 31, 2016 and 2015 the Company had options exercisable for 730,388 and 565,861 shares respectively, for which the weighted average exercise prices were $7.74 and $7.24, respectively. During the years ended December 31, 2017, 2016, and 2015 under all plans, the total intrinsic value of Vicor options exercised (i.e., the difference between the market price at exercise and the price paid by the employee to exercise the options) was $4,395,000, $1,392,000 and $928,000, respectively. The total amount of cash received by the Company from options exercised in 2017, 2016, and 2015, was $3,295,000, $1,572,000, and $805,000, respectively. The total grant-date fair value of stock options that vested during the years ended December 31, 2017, 2016, and 2015 was approximately $774,000, $365,000, and $1,194,000, respectively. As of December 31, 2017, there was $920,000 of total unrecognized compensation cost related to unvested non-performance The weighted-average fair value of Vicor options granted was $8.71, $4.94, and $6.76, in 2017, 2016, and 2015, respectively. Picor Stock Options A summary of the activity under the 2001 Picor Plan as of December 31, 2017 and changes during the year then ended, is presented below (in thousands except for share and weighted-average data): Options Weighted- Weighted- Aggregate Outstanding on December 31, 2016 9,530,987 $ 0.62 Granted 673,000 $ 0.62 Forfeited and expired (126,000 ) $ 0.73 Exercised (12,000 ) $ 0.41 Outstanding on December 31, 2017 10,065,987 $ 0.62 3.80 $ 493 Exercisable on December 31, 2017 8,384,987 $ 0.61 3.31 $ 400 Vested or expected to vest as of December 31, 2017(1) 9,996,810 $ 0.62 3.78 $ 492 (1) In addition to the vested options, the Company expects a portion of the unvested options to vest at some point in the future. Options expected to vest is calculated by applying an estimated forfeiture rate to the unvested options. As of December 31, 2016 and 2015, Picor had options exercisable for 7,915,219 and 8,053,490 shares, respectively, for which the weighted average exercise prices were $0.62 and $0.64, respectively. During the years ended December 31, 2017, 2016 and 2015, the total intrinsic value of Picor options exercised was $3,000, $24,000 and $72,000, respectively. The total amount of cash received by Picor from options exercised in 2017, 2016 and 2015 was $5,000, $17,000 and $14,000, respectively The total grant-date fair value of stock options that vested during the years ended December 31, 2017, 2016, and 2015 was approximately $180,000, $155,000, and $39,000, respectively. As of December 31, 2017, there was $322,000 of total unrecognized compensation cost related to unvested share-based awards for Picor. That cost is expected to be recognized over a weighted-average period of 3.1 years for all Picor awards. The expense will be recognized as follows: $117,000 in 2018, $83,000 in 2019, $61,000 in 2020, $45,000 in 2021, and $16,000 in 2022. The weighted-average fair value of Picor options granted was $0.27 in 2017, $0.26 in 2016, and $0.48 in 2015. VI Chip Stock Options A summary of the activity under the 2007 VI Chip Plan as of December 31, 2017 and changes during the year then ended, is presented below (in thousands except for share and weighted-average data): Options Weighted- Weighted- Aggregate Outstanding on December 31, 2016 9,933,750 $ 1.00 Granted 9,771,500 $ 0.96 Forfeited and expired (6,613,000 ) $ 1.00 Exercised — $ — Outstanding on December 31, 2017 (1) 13,092,250 $ 0.97 5.78 $ — Exercisable on December 31, 2017 810,700 $ 1.00 4.46 $ — Vested or expected to vest as of December 31, 2017(2) 11,210,701 $ 0.97 5.67 $ — (1) Of the total VI Chip options outstanding on December 31, 2017, 5,500,000 options had been granted to Dr. Vinciarelli, the Company’s Chief Executive Officer. (2) In addition to the vested options, the Company expects a portion of the unvested options to vest at some point in the future. Options expected to vest is calculated by applying an estimated forfeiture rate to the unvested options. As of December 31, 2016 and 2015, VI Chip had options exercisable for 7,074,650 and 7,042,600 shares, respectively, for which the weighted average exercise price was $1.00. There were no VI Chip options exercised in 2017 and 2016. The total intrinsic value of VI Chip options exercised in 2015 was zero. The total amount of cash received by VI Chip from options exercised in 2015 was $1,000. The total grant-date fair value of stock options that vested during the years ended December 31, 2017, 2016, and 2015 was approximately $2,900,000, $0, and $1,000, respectively. As of December 31, 2017, there was $2,395,000 of total unrecognized compensation cost related to unvested share-based awards for VI Chip. That cost is expected to be recognized over a weighted-average period of 4.0 years for all VI Chip awards. The expense will be recognized as follows: $603,000 in 2018, $544,000 in 2019, $503,000 in 2020, $483,000 in 2021, and $262,000 in 2022. The weighted-average fair value of VI Chip options granted was $0.29, $0.01, and $0.01 in 2017, 2016, and 2015, respectively. 401(k) Plan The Company sponsors a savings plan available to all domestic employees, which qualifies under Section 401(k) of the Internal Revenue Code. Employees may contribute to the plan in amounts representing from 1% to 80% of their pre-tax Stock Bonus Plan Under the Company’s 1985 Stock Bonus Plan, as amended, shares of Common Stock may be awarded to employees from time to time as determined by the Board of Directors. On December 31, 2017, 109,964 shares were available for further award. All shares awarded to employees under this plan have vested. No further awards are contemplated under this plan at the present time.

Long-Term Investments

Long-Term Investments	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Long-Term Investments	4. LONG-TERM INVESTMENTS As of December 31, 2017 and 2016, the Company held one auction rate security with a par value of $3,000,000, purchased through and held in custody by a broker-dealer affiliate of Bank of America, N.A., that has experienced failed auctions (the “Failed Auction Security”) since February 2008. The Failed Auction Security held by the Company is Aaa/AA+ rated by major credit rating agencies, is collateralized by student loans, and is guaranteed by the U.S. Department of Education under the Federal Family Education Loan Program. Management is not aware of any reason to believe the issuer of the Failed Auction Security is presently at risk of default. Through December 31, 2017, the Company has continued to receive interest payments on the Failed Auction Security in accordance with the terms of its indenture. Management believes the Company ultimately should be able to liquidate the Failed Auction Security without significant loss primarily due to the overall quality of the issue held and the collateral securing the substantial majority of the underlying obligation. However, current conditions in the auction rate securities market have led management to conclude the recovery period for the Failed Auction Security exceeds 12 months. As a result, the Company continued to classify the Failed Auction Security as long-term as of December 31, 2017. The following is a summary of available-for-sale December 31, 2017 Cost Gross Gross Estimated Fair Failed Auction Security $ 3,000 $ — $ 475 $ 2,525 December 31, 2016 Cost Gross Gross Estimated Fair Failed Auction Security $ 3,000 $ — $ 492 $ 2,508 As of December 31, 2017 and 2016, the Failed Auction Security had been in an unrealized loss position for greater than 12 months. The amortized cost and estimated fair value of available-for-sale Cost Estimated Fair Due in twenty to forty years $ 3,000 $ 2,525 Based on the fair value measurements described in Note 5, the fair value of the Failed Auction Security on December 31, 2017, with a par value of $3,000,000, was estimated by the Company to be approximately $2,525,000. The gross unrealized loss of $475,000 on the Failed Auction Security consists of two types of estimated loss: an aggregate credit loss of $48,000 and an aggregate temporary impairment of $427,000. In determining the amount of credit loss, the Company compared the present value of cash flows expected to be collected to the amortized cost basis of the security, considering credit default risk probabilities and changes in credit ratings as significant inputs, among other factors (see Note 5). The following table represents a rollforward of the activity related to the credit loss recognized in earnings on available-for-sale 2017 2016 2015 Balance at the beginning of the period $ 59 $ 72 $ 84 Reductions in the amount related to credit gain for which other-than-temporary impairment was not previously recognized (11 ) (13 ) (12 ) Balance at the end of the period $ 48 $ 59 $ 72 At this time, the Company has no intent to sell the Failed Auction Security and does not believe it is more likely than not the Company will be required to sell the security. If current market conditions deteriorate further, the Company may be required to record additional unrealized losses. If the credit rating of the security deteriorates, the Company may be required to adjust the carrying value of the investment through impairment charges recorded in the Consolidated Statement of Operations, and any such impairment adjustments may be material. Based on the Company’s ability to access cash and cash equivalents and its expected operating cash flows, management does not anticipate the current lack of liquidity associated with the Failed Auction Security held will affect the Company’s ability to execute its current operating plan.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	5. FAIR VALUE MEASUREMENTS The Company accounts for certain financial assets at fair value, defined as the price that would be received to sell an asset or paid to transfer a liability (i.e., an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions market participants would use in pricing an asset or liability. A three-level hierarchy is used to show the extent and level of judgment used to estimate fair value measurements. Assets and liabilities measured at fair value on a recurring basis included the following as of December 31, 2017 (in thousands): Using Quoted Prices Significant Significant (Level 3) Total Fair Cash equivalents: Money market funds $ 9,279 $ — $ — $ 9,279 Long-term investments: Failed Auction Security — — 2,525 2,525 Liabilities: Contingent consideration obligations — — (678 ) (678 ) Assets measured at fair value on a recurring basis included the following as of December 31, 2016 (in thousands): Using Quoted Prices Significant Significant Total Fair Cash equivalents: Money market funds $ 10,114 $ — $ — $ 10,114 Long-term investments: Failed Auction Security — — 2,508 2,508 Liabilities: Contingent consideration obligation — — (253 ) (253 ) As of December 31, 2017, there was insufficient observable auction rate security market information available to determine the fair value of the Failed Auction Security using Level 1 or Level 2 inputs. As such, the Company’s investment in the Failed Auction Security was deemed to require valuation using Level 3 inputs. Management, after consulting with advisors, valued the Failed Auction Security using analyses and pricing models similar to those used by market participants (i.e., buyers, sellers, and the broker-dealers responsible for execution of the Dutch auction pricing mechanism by which each issue’s interest rate was set). Management utilized a probability weighted discounted cash flow (“DCF”) model to determine the estimated fair value of this security as of December 31, 2017. The major assumptions used in preparing the DCF model included: estimates for the amount and timing of future interest and principal payments based on default probability assumptions used to measure the credit loss of 2.0%; the rate of return required by investors to own this type of security in the current environment, which we estimate to be 5.0% above the risk free rate of return; and an estimated time frame of three to five years for successful auctions for this type of security to occur. In making these assumptions, management considered relevant factors including: the formula applicable to each security defining the interest rate paid to investors in the event of a failed auction (the “Penalty Rate”); forward projections of the interest rate benchmarks specified in such formulas; the likely timing of principal repayments; the probability of full repayment considering the guarantees by the U.S. Department of Education of the underlying student loans, guarantees by other third parties, and additional credit enhancements provided through other means; and publicly available pricing data for recently issued student loan asset-backed securities not subject to auctions. In developing its estimate of the rate of return required by investors to own these securities, management compared the Penalty Rate of the Failed Auction Security with yields of actively traded long-term bonds with similar characteristics and, reflecting the limited liquidity for auction rate securities and the discounts to par value seen in recent tender offers by issuers and arm’s length market transactions between informed buyers and sellers, estimated the implied yield (i.e., the discount to par value) necessary to complete a sale of the Failed Auction Security. Management has calculated an increase or decrease in the liquidity risk premium of 5.0% referenced above of 1.0% (i.e., 100 basis points) as used in the model, would decrease or increase, respectively, the fair value of the Failed Auction Security by approximately $100,000. The significant unobservable inputs used in the fair value measurement of the Company’s Failed Auction Security are the cumulative probability of earning the maximum rate until maturity, the cumulative probability of principal return prior to maturity, the cumulative probability of default, the liquidity risk premium, and the recovery rate in default. Significant increases (decreases) in any of those inputs in isolation would result in changes in fair value measurement. Significant increases (decreases) in the cumulative probability of earning the maximum rate until maturity, the cumulative probability of principal return prior to maturity, and the recovery rate in default would result in a higher (lower) fair value measurement, while increases (decreases) in the cumulative probability of default and the liquidity risk premium would result in a (lower) higher fair value measurement. Generally, the interrelationships are such that a change in the assumption used for the cumulative probability of principal return prior to maturity is accompanied by a directionally similar change in the assumption used for the cumulative probability of earning the maximum rate until maturity and a directionally opposite change in the assumptions used for the cumulative probability of default and the liquidity risk premium. The recovery rate in default is somewhat independent and based upon the securities’ specific underlying assets and published recovery rate indices. Quantitative information about Level 3 fair value measurements as of December 31, 2017 are as follows (dollars in thousands): Fair Valuation Unobservable Input Weighted Failed Auction Security $ 2,525 Discounted Cumulative probability of earning the maximum rate until maturity 0.06 % Cumulative probability of principal return prior to maturity 93.71 % Cumulative probability of default 6.24 % Liquidity risk premium 5.00 % Recovery rate in default 40.00 % The change in the estimated fair value calculated for the investment valued on a recurring basis utilizing Level 3 inputs (i.e., the Failed Auction Security) for the year ended December 31, 2017 was as follows (in thousands): Balance at the beginning of the period $ 2,508 Credit gain on available-for-sale 11 Gain included in Other comprehensive income (loss) 6 Balance at the end of the period $ 2,525 The Company has classified its contingent consideration obligations as Level 3 because the fair value for this liability was determined using unobservable inputs. The liability was based on estimated sales of legacy products over the period of royalty payments at the royalty rate (see Note 9), discounted using the Company’s estimated cost of capital. The change in the estimated fair value calculated for the liabilities valued on a recurring basis utilizing Level 3 inputs (i.e., the Contingent consideration obligations) for the year ended December 31, 2017 was as follows (in thousands): Balance at the beginning of the period $ 253 Increase in estimated contingent consideration obligations (see Note 9) 650 Payments (225 ) Balance at the end of the period $ 678 There were no transfers between Level 1 and Level 2 of the fair value hierarchy during the year ended December 31, 2017.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Inventories	6. INVENTORIES Inventories as of December 31 were as follows (in thousands): 2017 2016 Raw materials $ 27,400 $ 18,648 Work-in-process 3,596 3,361 Finished goods 5,503 5,127 Net balance $ 36,499 $ 27,136

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	7. PROPERTY, PLANT AND EQUIPMENT Property, plant and equipment are stated at cost and are depreciated and amortized over a period of three to 39 years generally under the straight-line method for financial reporting purposes and accelerated methods for income tax purposes. Property, plant and equipment as of December 31 were as follows (in thousands): 2017 2016 Land $ 2,089 $ 2,089 Buildings and improvements 45,147 43,950 Machinery and equipment 243,392 237,434 Furniture and fixtures 6,320 5,656 Construction in-progress 4,120 2,471 301,068 291,600 Accumulated depreciation and amortization (259,712 ) (254,026 ) Net balance $ 41,356 $ 37,574 Depreciation expense for the years ended December 31, 2017, 2016 and 2015 was approximately $8,763,000, $8,304,000, and $9,028,000 respectively. As of December 31, 2017, the Company had approximately $1,911,000 of capital expenditure commitments.

Other Investments

Other Investments	12 Months Ended
	Dec. 31, 2017
Text Block [Abstract]
Other Investments	8. OTHER INVESTMENTS In September 2015, Intersil Corporation (“Intersil”) acquired, through a statutory merger, Great Wall Semiconductor Corporation (“GWS”), in which the Company held non-voting At the time of the merger transaction, the Company’s gross investment totaled $4,999,719. However, during the fourth quarter of 2008, the Company determined a decline in value judged to be other-than-temporary had occurred and, as such, the investment’s recorded value on the Consolidated Balance Sheet, as of December 31, 2008, was reduced to zero. Management’s decision to reduce the remaining investment balance to zero at that time was based on GWS’ continued operating losses, the impact of the global economic crisis on the current and short-term outlook for its operations, a negative working capital position as of December 31, 2008, and a valuation based on discounted cash flows. Under the terms of the merger agreement between GWS and Intersil, and in accordance with the terms of the shareholder agreement under which the Company made its investments, all preferred stock was redeemed at full preference value (i.e., purchased for cash equal to the original investment amount). Therefore, the Company’s gross investment value of $4,999,719 was recorded as a Gain from sales of equity method investment, net of tax in the Consolidated Statements of Operations. The Company and GWS were parties to an intellectual property cross-licensing agreement, a license agreement, and two supply agreements, under which the Company purchased certain components from GWS. Intersil, through the merger transaction, has assumed all of GWS’ rights and obligations under these agreements. Company purchases from GWS totaled approximately $1,662,000 for the nine months ended September 30, 2015, the approximate time of the sale.

Noncontrolling Interest Transac

Noncontrolling Interest Transactions	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Noncontrolling Interest Transactions	9. NONCONTROLLING INTEREST TRANSACTIONS On March 30, 2016, the Company acquired 100% ownership of certain operating assets and cash of its consolidated subsidiary, Converpower Corporation (“Converpower”), in which it held a 49% ownership interest. The operating assets and cash were acquired in exchange for the Company’s common shares representing that 49% interest and the aggregate dollar amount of royalty payments to be made by the Company to Converpower. The transaction was executed through a newly-formed, wholly-owned subsidiary, Granite Power Technologies, Inc. (“GPT”), the business operations of which had formerly existed as a division of Vicor Corporation. The shares of Converpower common stock held by the Company were contributed to GPT prior to the transaction. At the same time that it entered into the Asset Purchase Agreement associated with this transaction, the Company and Converpower entered into a license agreement providing the Company the right to continue manufacturing certain Converpower products in exchange for payment of royalties, quarterly through June 30, 2021, equal to a percentage of the revenue generated by the manufacture and sale of these products by GPT. The estimated present value of total future royalties, included in “Contingent consideration obligations” in the accompanying Consolidated Balance Sheet as of December 31, 2017, is $478,000 (initially $208,000, as of March 31, 2016). The Company increased the liability by approximately $448,000 in 2017 based on a reassessment of the total obligation through the end of license agreement. The amount was included in selling, general, and administrative expenses. Although the Company exchanged its shares representing its 49% equity interest in Converpower, it acquired 100% control of the business operations. Accordingly, this transaction was accounted for as an acquisition of a noncontrolling interest (i.e., an equity transaction). As such, the noncontrolling interest balance in equity associated with Converpower was reduced to zero, and the additional paid-in On December 28, 2015, the Company sold its 49% ownership interest in Aegis Power Systems, Inc. (“APS”) to the 51% noncontrolling interest holder for approximately $1,698,000. The amount of the proceeds approximated the Company’s share of the net equity of APS, resulting in a gain of approximately $28,000, which was recorded in Other income (expense), net in the accompanying Consolidated Statements of Operations. As a result of the transaction, cash of approximately $2,090,000 and other net assets of approximately $1,317,000 of APS were fully deconsolidated from the Company’s consolidated balance sheet as of December 31, 2015. After the sale, APS operates independently from the Company, and may purchase the Company’s products going forward, on an arms-length basis. Also on December 28, 2015, the Company acquired the noncontrolling interest holder’s 18% ownership interest in Mission Power Solutions, Inc. (“MPS”) for approximately $216,000, which equaled the noncontrolling interest holder’s share of the net equity of MPS. This transaction was achieved through a statutory merger of MPS with and into an existing Vicor Custom Power wholly-owned subsidiary, Northwest Power, Inc. (“NPI”). In addition to the payment noted above, the selling principal will be eligible to receive quarterly royalty payments through June 30, 2021 equal to a percentage of the revenue generated by the sale of certain MPS legacy products to be manufactured by NPI going forward. The estimated obligation for total future royalties, recorded as Contingent consideration obligation in the accompanying Consolidated Balance Sheets as of December 31, 2017 is $200,000 (initially $144,000 as of December 31, 2015). The Company increased the liability by approximately $202,000 in 2017, based on a reassessment of the total obligation under the royalty arrangement. The amount was included in selling, general, and administrative expenses. The acquisition of the noncontrolling interest holder’s 18% ownership interest was accounted for as an equity transaction, and therefore, the noncontrolling interest balance in equity for this subsidiary was reduced to zero. The excess of the acquisition amount, which is inclusive of the cash paid and the value of the contingent consideration obligation, over the noncontrolling interest balance in equity, was recorded as a charge to additional paid-in The respective noncontrolling interest holders of APS, Converpower, and MPS served as key employees of each company prior to the transactions described above.

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	10. INTANGIBLE ASSETS Patent costs, which are included in other assets in the accompanying Consolidated Balance Sheets, as of December 31 were as follows (in thousands): 2017 2016 Patent costs $ 2,093 $ 2,427 Accumulated amortization (1,386 ) (1,598 ) $ 707 $ 829 Definite lived intangible assets, such as patent rights, are amortized and tested for impairment if a triggering event occurs. Amortization expense was approximately $130,000, $134,000 and $145,000 in 2017, 2016 and 2015, respectively. The estimated future amortization expense from patent assets held as of December 31, 2017, is projected to be $112,000, $107,000, $102,000, $93,000 and $61,000, in fiscal years 2018, 2019, 2020, 2021, and 2022, respectively.

Product Warranties

Product Warranties	12 Months Ended
	Dec. 31, 2017
Guarantees and Product Warranties [Abstract]
Product Warranties	11. PRODUCT WARRANTIES Product warranty activity for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Balance at the beginning of the period $ 214 $ 585 $ 204 Accruals for warranties for products sold in the period 346 358 715 Fulfillment of warranty obligations (194 ) (527 ) (334 ) Revisions of estimated obligations (76 ) (202 ) — Balance at the end of the period $ 290 $ 214 $ 585

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	12. STOCKHOLDERS’ EQUITY Each share of Common Stock entitles the holder thereof to one vote on all matters submitted to the stockholders. Each share of Class B Common Stock entitles the holder thereof to ten votes on all such matters. Shares of Class B Common Stock are not transferable by a stockholder except to or among the stockholder’s spouse, certain of the stockholder’s relatives, and certain other defined transferees. Class B Common Stock is not listed or traded on any exchange or in any market. Class B Common Stock is convertible at the option of the holder thereof at any time and without cost to the stockholder into shares of Common Stock on a one-for-one In November 2000, the Board of Directors of the Company authorized the repurchase of up to $30,000,000 of the Company’s Common Stock (the “November 2000 Plan”). The plan authorizes the Company to make repurchases from time to time in the open market or through privately negotiated transactions. The timing of this program and the amount of the stock that may be repurchased is at the discretion of management based on its view of economic and financial market conditions. There were no repurchases under the November 2000 Plan in 2017, 2016, and 2015. On December 31, 2017, the Company had approximately $8,541,000 available for share repurchases under the November 2000 Plan. Dividends are declared at the discretion of the Company’s Board of Directors and depend on actual cash from operations, the Company’s financial condition and capital requirements and any other factors the Company’s Board of Directors may consider relevant at the time. Common Stock and Class B Common Stock participate in dividends and earnings equally. During the years ended December 31, 2016 and 2015, one subsidiary paid a total of $750,000 and $250,000, in cash dividends, respectively, all of which were paid to the Company. On December 31, 2017, 2016, and 2015, there were 21,976,340, 14,377,880, and 14,594,805, respectively, shares of Vicor Common Stock reserved for issuance upon exercise of Vicor stock options, upon conversion of Class B Common Stock and under the ESPP.

Other Income (Expense), Net

Other Income (Expense), Net	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Other Income (Expense), Net	13. OTHER INCOME (EXPENSE), NET The major changes in the components of Other income (expense), net for the years ended December 31 were as follows (in thousands): 2017 2016 2015 Rental income $ 792 $ 462 $ — Foreign currency gains (losses), net 323 (268 ) (161 ) Interest income 124 68 47 Gain (loss) on disposal of equipment 14 (4 ) 60 Credit gains on available-for-sale 11 13 12 Other (2 ) 13 67 $ 1,262 $ 284 $ 25 During the second quarter of 2016, the Company began recognizing rental income under a leasing agreement with a third party for its facility in Sunnyvale, California.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	14. INCOME TAXES The tax provision includes estimated federal, state and foreign income taxes on the Company’s pre-tax On December 22, 2017, the U.S. government enacted comprehensive tax legislation, referred to as the Tax Cuts and Jobs Act (the “Tax Act”). The Tax Act makes broad and complex changes to the U.S. tax code, including, but not limited to: (1) reducing the U.S. federal corporate tax rate from 35% to 21%; (2) elimination of the corporate alternative minimum tax (“AMT”) and changing how existing AMT credits can be realized; (3) changing rules related to the usage and limitation of net operating loss carryforwards created in tax years beginning after December 31, 2017; and (4) implementing a territorial tax system, which generally eliminates the U.S. federal income tax on dividends from foreign subsidiaries, and imposes a one-time U.S. GAAP requires the impact of tax legislation to be recorded in the period of enactment. The Tax Act, though, did not have a significant impact on the Company’s consolidated financial statements, primarily because it continues to maintain a full valuation allowance against all domestic net deferred tax assets, as discussed below. While the Company re-measured one-time one-time Certain impacts of the Tax Act would generally require accounting to be completed in the period of enactment. However, in response to the complexities of the Tax Act, the Securities and Exchange Commission (“SEC”) issued guidance through Staff Accounting Bulletin No. 118 to provide companies with relief. Specifically, when the initial accounting for items under the Tax Act is incomplete, the guidance allows companies to include provisional amounts when reasonable estimates can be made. The SEC has provided up to a one-year re-measurement one-time The reconciliation of the federal statutory rate on the loss before income taxes and before the gain from sale of equity method investment to the effective income tax rate for the years ended December 31 is as follows: 2017 2016 2015 Statutory federal tax rate (34.0 )% (34.0 )% (34.0 )% State income taxes, net of federal income tax benefit 97.2 1.9 46.4 Rate change due to tax reform 3,441.1 — — Tax credits (1,222.3 ) (13.6 ) 29.9 Increase (decrease) in valuation allowance (936.1 ) 46.5 (138.4 ) Permanent items (861.2 ) 0.9 21.2 Refundable income taxes — AMT credit (751.0 ) — — Foreign rate differential and deferred items (91.8 ) (0.8 ) (18.2 ) Decrease in tax reserves (5.1 ) — (248.6 ) Capital gain on sale to noncontrolling interest — 3.9 237.8 Decrease in unremitted Vicor Custom Power earnings — (0.9 ) (108.7 ) Book income attributable to noncontrolling interest — 0.1 47.0 Other (0.1 ) (0.2 ) (0.1 ) (363.3 )% 3.8 % (165.7 )% In 2017, 2016, and 2015, the Company did not recognize a tax benefit for the majority of its losses as it maintained a full valuation allowance against all net domestic deferred tax assets due to the inability to project net future taxable income, as described below. In 2017, the benefit for income taxes was primarily due to the Company’s AMT credit carryforwards of approximately $736,000 becoming fully refundable in future years, due to the repeal of the corporate AMT under the Tax Act. In 2016, in connection with the Company’s acquisition of 100% ownership of certain operating assets and cash of Converpower, the related deferred tax liability for unremitted earnings of $55,000 was reversed and recorded as a discrete benefit in the first quarter of 2016 (see Note 9). In 2015, the Company entered into voluntary disclosure agreements with several states. As a result, the Company recognized a tax benefit of approximately $555,000 as a discrete item in the fourth quarter of 2015 for the release of tax reserves. In addition, in connection with the Company’s sale of its 49% interest in APS, recognized as a capital gain, the related deferred tax liability for unremitted earnings of $274,000 was reversed and recorded as a deferred tax benefit in the fourth quarter of 2015 (see Note 9). For financial reporting purposes, income (loss) before income taxes and before the gain from sale of equity method investment for the years ended December 31 include the following components (in thousands): 2017 2016 2015 Domestic $ (1,591 ) $ (6,034 ) $ 1,373 Foreign 1,493 4 (1,615 ) $ (98 ) $ (6,030 ) $ (242 ) Significant components of the provision (benefit) for income taxes for the years ended December 31 are as follows (in thousands): 2017 2016 2015 Current: Federal $ (736 ) $ — $ 144 State 156 172 (473 ) Foreign 396 137 111 (184 ) 309 (218 ) Deferred: Federal — (55 ) (274 ) Foreign (172 ) (23 ) 91 (172 ) (78 ) (183 ) $ (356 ) $ 231 $ (401 ) As discussed in Note 8, the Company recorded a gain from equity method investment in the third quarter of 2015 for cash consideration received equal to its gross investment in GWS of $4,999,719 for the full preference value of its non-voting The Tax Act eliminates the deferral of U.S. income tax on accumulated foreign earnings by imposing a one-time As noted above, the change in the U.S. federal corporate tax rate, which is effective January 1, 2018, is reflected in the Company’s deferred tax table below. Significant components of the Company’s deferred tax assets and liabilities as of December 31 were as follows (in thousands): 2017 2016 Deferred tax assets: Research and development tax credit carryforwards $ 20,019 $ 13,967 Net operating loss carryforwards 4,918 4,902 Stock-based compensation 2,793 4,066 Investment tax credit carryforwards 2,181 1,576 Inventory reserves 2,059 3,143 Vacation accrual 1,255 1,928 Contingent consideration liabilities 148 — Unrealized loss on investments 135 136 Deferred revenue 79 154 Warranty reserves 45 73 Bad debt reserves 36 52 Alternative minimum tax credit carryforward — 340 Other 273 331 Total deferred tax assets 33,941 30,668 Less: Valuation allowance for deferred tax assets (33,024 ) (29,274 ) Net deferred tax assets 917 1,394 Deferred tax liabilities: Prepaid expenses (470 ) (654 ) Patent amortization (161 ) (296 ) Depreciation (76 ) (406 ) Total deferred tax liabilities (707 ) (1,356 ) Net deferred tax assets (liabilities) $ 210 $ 38 As of December 31, 2017, the Company has a valuation allowance of approximately $33,024,000 against all domestic net deferred tax assets, for which realization cannot be considered more likely than not at this time. Management assesses the need for the valuation allowance on a quarterly basis. In assessing the need for a valuation allowance, the Company considers all positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax planning strategies, and past financial performance. The Company remains in a significant cumulative loss position as of December 31, 2017 and, as a result, management believes a full valuation allowance against all domestic net deferred tax assets is warranted as of December 31, 2017. The valuation allowance against these deferred tax assets may require adjustment in the future based on changes in the mix of temporary differences, changes in tax laws, and operating performance. If and when the Company determines the valuation allowance should be released (i.e., reduced), the adjustment would result in a tax benefit reported in that period’s Consolidated Statements of Operations, the effect of which would be an increase in reported net income. As described in Note 2 — Impact of recently issued accounting standards The research and development tax credit carryforwards of approximately $11,711,000 and $11,714,000, respectively, expire beginning in 2018 for state purposes and in 2022 for federal purposes. The Company has federal net operating loss carryforwards of approximately $18,351,000, which expire beginning in 2033, as well as net operating loss carryforwards in certain states of approximately $28,770,000, which expire beginning in 2018 through 2037. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): 2017 2016 2015 Balance on January 1 $ 946 $ 830 $ 1,254 Additions based on tax positions related to the current year 138 125 120 Additions for tax positions of prior years 29 — — Settlements (1 ) — (480 ) Lapse of statute (8 ) (9 ) (64 ) Balance on December 31 $ 1,104 $ 946 $ 830 The Company has reviewed the tax positions taken, or to be taken, in its tax returns for all tax years currently open to examination by a taxing authority. The total amount of unrecognized tax benefits, that is the aggregate tax effect of differences between tax return positions and the benefits recognized in the Company’s financial statements, as of December 31, 2017, 2016, and 2015 of $1,104,000, $946,000, and $830,000, respectively, if recognized, may decrease the Company’s income tax provision and effective tax rate. None of the unrecognized tax benefits as of December 31, 2017, are expected to significantly change during the next twelve months. The Company recognizes accrued interest and penalties, if any, related to unrecognized tax benefits as a component of income tax expense. During the years ended December 31, 2017, 2016, and 2015, the Company recognized approximately $6,000, $6,000, and $21,000, respectively, in net interest expense. As of December 31, 2017 and 2016, the Company had accrued approximately $29,000 and $25,000, respectively, for the potential payment of interest. The Company files income tax returns in the United States and various foreign tax jurisdictions. These tax returns are generally open to examination by the relevant tax authorities from three to seven years from the date they are filed. The tax filings relating to the Company’s federal and state taxes are currently open to examination for tax years 2014 and 2016 and 2008 through 2016, respectively. In addition, the 2003, 2004, and 2007 tax years resulted in losses. These years may also be subject to examination since the losses were carried forward and utilized in future years. The Company’s subsidiary in Italy, Vicor Italy S.r.l. (“Vicor Italy”), underwent during 2014 a tax inspection for tax years 2009 through 2013, covering corporation, regional and value added taxes. Vicor Italy received a preliminary tax audit report dated June 30, 2014. The Company filed a response to the preliminary tax audit report in the third quarter of 2014. The statute of limitations for the tax authorities in Italy to file an assessment, if any, expired on December 31, 2015 for tax year 2009, on December 31, 2016 for tax year 2010, and on December 31, 2017 for tax year 2011. While management believes it is too early to determine the likelihood or amount of potential liability at this time, it does not believe the ultimate impact of this matter will be material to the Company’s financial statements. In May 2017, the Company received notice from the Internal Revenue Service that its federal corporate tax return for tax year 2015 had been selected for examination. The examination is ongoing. In January 2018, the Company received notice from the New York State Department of Taxation and Finance that its New York State tax returns for tax years 2014 through 2016 were selected for audit. On site fieldwork for this audit will take place in March 2018. There are no other income tax examinations or audits currently in process.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	15. COMMITMENTS AND CONTINGENCIES The Company leases certain of its office and manufacturing space. The future minimum rental commitments under non-cancelable Year 2018 $ 1,742 2019 1,152 2020 872 2021 467 2022 and thereafter 1,002 Rent expense was approximately $1,889,000, $1,866,000 and $1,902,000 in 2017, 2016 and 2015, respectively. The Company also pays tenant-related executory costs such as taxes, maintenance, and insurance. On January 28, 2011, SynQor, Inc. (“SynQor”) filed a complaint for patent infringement against Ericsson, Inc. (“Ericsson”), Cisco Systems, Inc. (“Cisco”) and the Company in the U.S. District Court for the Eastern District of Texas (the “Texas Action”). Ericsson and Cisco subsequently settled with SynQor and are no longer parties to the Texas Action. With respect to the Company, SynQor’s complaint in the Texas Action alleged that the Company’s products, including but not limited to unregulated bus converters used in intermediate bus architecture power supply systems, infringe SynQor’s U.S. patent numbers 7,072,190, 7,272,021, and 7,564,702 (“the ‘190 patent”, “the ‘021 patent” and “the ‘702 patent”, respectively). SynQor’s complaint sought an injunction against further infringement and an award of unspecified compensatory and enhanced damages, interest, costs and attorney fees. On September 20, 2011, SynQor filed an amended complaint in the Texas Action that further alleged that the Company’s products, including, but not limited to, unregulated bus converters used in intermediate bus architecture power supply systems, infringe SynQor’s U.S. patent number 8,023,290 (“the ‘290 patent”). The Company responded to SynQor’s amended complaint in the Texas Action by denying its products infringe any of the SynQor patents, and asserting that the SynQor patents are invalid. The Company further alleged that the SynQor ‘290 patent is unenforceable due to inequitable conduct by SynQor or its agents during the examination of the ‘290 patent at the United States Patent and Trademark Office (“USPTO”). The Company also asserted counterclaims seeking damages against SynQor for deceptive trade practices and tortious interference with prospective economic advantage arising from SynQor’s attempted enforcement of its patents against the Company. The Company initiated administrative review proceedings at the USPTO challenging the validity of certain claims of the SynQor patents asserted in the Texas Action, including all claims that were asserted against the Company by SynQor. Regarding the ‘190 patent, the Patent Trial and Appeal Board (“PTAB”) of the USPTO issued a decision upholding the validity of the ‘190 patent claims. That decision was appealed by the Company to the United States Court of Appeals for the Federal Circuit (“the Federal Circuit”), which issued a decision on March 13, 2015 reversing the PTAB, determining that certain claims were invalid, and remanding the matter to the PTAB for further proceedings. On May 2, 2016, the PTAB issued a decision determining that all but one of the remaining claims of the ‘190 patent were invalid and remanding the remaining claim to a patent examiner for further examination. On June 22, 2017, the examiner issued a determination under 37 C.F.R. § 41.77(d), finding that the remaining claim of the ‘190 patent was unpatentable. That decision is expected to be further reviewed by the PTAB pursuant to 37 C.F.R. § 41.77(f). On May 2, 2016, the PTAB also issued decisions finding all challenged claims of SynQor’s ‘021 patent invalid and upholding the validity of all challenged claims of SynQor’s ‘702 and ‘290 patents. On May 23, 2016, the Texas Court issued an order staying the Texas Action until the completion of all of the administrative review proceedings concerning the asserted SynQor patents, including any appeals from such proceedings to the Federal Circuit. On August 30, 2017, the Federal Circuit issued rulings with regard to PTAB’s reexamination decisions for the ‘021, ‘702 and ‘290 patents. With respect to the ‘021 patent, the Federal Circuit affirmed the PTAB’s determination that all of the challenged claims of the ‘021 patent were invalid. The Federal Circuit remanded the case to the PTAB for further consideration of the patentability of certain claims that had been added by amendment during the reexamination. With respect to the ‘702 patent, the Federal Circuit affirmed the PTAB’s determination that all of the challenged claims of the ‘702 patent were patentable. With respect to the ‘290 patent, the Federal Circuit vacated the PTAB’s decision upholding the patentability of the ‘290 patent claims, and remanded the case to the PTAB for further consideration. On October 31, 2017, the Company filed a request with the USPTO for ex parte reexamination of the ‘702 patent, based on different prior art references than had been at issue in the previous inter parte reexamination of the ‘702 patent. On December 6, 2017, the USPTO issued a decision granting the Company’s request for ex parte reexamination of the ‘702 patent, finding that the Company’s request was warranted because it raised substantial new questions of patentability of the ‘702 patent. The Company continues to believe none of its products, including its unregulated bus converters, infringe any valid claim of the asserted SynQor patents, either alone or when used in an intermediate bus architecture implementation. The Company believes SynQor’s claims lack merit and, therefore, continues to vigorously defend itself against SynQor’s patent infringement allegations. The Company does not believe a loss is probable for this matter. If a loss were to be incurred, however, the Company cannot estimate the amount of possible loss or range of possible loss at this time. In addition to the SynQor matter, the Company is involved in certain other litigation and claims incidental to the conduct of its business. While the outcome of lawsuits and claims against the Company cannot be predicted with certainty, management does not expect any current litigation or claims will have a material adverse impact on the Company’s financial position or results of operations.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Information	16. SEGMENT INFORMATION The Company has organized its business segments according to its key product lines. The BBU segment designs, develops, manufactures, and markets the Company’s modular DC-DC The Company’s Chief Executive Officer (i.e., the chief operating decision maker) evaluates performance and allocates resources based on segment revenues and segment operating income (loss). The operating income (loss) for each segment includes selling, general, and administrative and research and development expenses directly attributable to the segment. Certain of the Company’s indirect overhead costs, which include corporate selling, general, and administrative expenses, are allocated among the segments based upon an estimate of costs associated with each segment. Assets allocated to each segment are based upon specific identification of such assets, which include accounts receivable, inventories, fixed assets and certain other assets. The Corporate segment consists of those operations and assets shared by all segments. The costs of certain centralized executive and administrative functions are recorded in this segment, as are certain shared assets, most notably cash and cash equivalents, deferred tax assets, long-term investments, the Company’s facilities in Massachusetts, real estate, and other assets. The Company’s accounting policies and method of presentation for segments are consistent with that used throughout the Consolidated Financial Statements. The following table provides significant segment financial data as of and for the years ended December 31 (in thousands): BBU VI Chip Picor Corporate Eliminations Total (1) 2017: Net revenues $ 151,789 $ 61,330 $ 26,297 $ — $ (11,586 ) $ 227,830 Income (loss) from operations 5,615 (11,495 ) 5,400 (880 ) — (1,360 ) Total assets 232,255 34,809 13,509 59,550 (174,399 ) 165,724 Depreciation and amortization 3,907 2,782 747 1,457 — 8,893 2016: Net revenues $ 151,428 $ 39,947 $ 16,684 $ — $ (7,779 ) $ 200,280 Income (loss) from operations 11,750 (16,494 ) (637 ) (933 ) — (6,314 ) Total assets 196,987 21,389 8,583 73,253 (146,145 ) 154,067 Depreciation and amortization 4,258 2,235 545 1,400 — 8,438 2015: Net revenues $ 173,064 $ 36,688 $ 17,304 $ — $ (6,862 ) $ 220,194 Income (loss) from operations 21,743 (21,040 ) (290 ) (680 ) — (267 ) Total assets 170,939 15,577 5,369 81,824 (116,164 ) 157,545 Depreciation and amortization 4,538 2,740 442 1,422 — 9,142 (1) The elimination for net revenues is principally related to inter-segment revenues of Picor to BBU and VI Chip and for inter-segment revenues of VI Chip to BBU. The elimination for total assets is principally related to inter-segment accounts receivable due to BBU for the funding of VI Chip and Picor operations. During 2017, 2016, and 2015, one customer accounted for approximately 13.0%, 16.4%, and 16.2% of net revenues, respectively, which were included in all three business segments in each of the three years. Net revenues from unaffiliated customers by country, based on the location of the customer, for the years ended December 31 were as follows (in thousands): 2017 2016 2015 United States $ 83,871 $ 80,603 $ 88,136 Europe 24,078 22,495 29,686 Asia Pacific 114,365 91,848 94,845 All other 5,516 5,334 7,527 $227,830 $200,280 $220,194 Net revenues from customers in China (including Hong Kong), our largest international market, accounted for approximately 35.8% of total net revenues in 2017, 32.1% in 2016 and 34.2% in 2015, respectively.

Quarterly Results of Operations

Quarterly Results of Operations (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Results of Operations (Unaudited)	17. QUARTERLY RESULTS OF OPERATIONS (Unaudited) The following table sets forth certain unaudited quarterly financial data for the years ended December 31 (in thousands, except per share amounts): First Second Third Fourth Total 2017: Net revenues $ 54,462 $ 57,709 $ 56,888 $ 58,771 $ 227,830 Gross margin 23,652 25,930 25,143 26,931 101,656 Consolidated net income (loss) (954 ) (445 ) 38 1,619 258 Net income attributable to noncontrolling interest 20 14 49 8 91 Net income (loss) attributable to Vicor Corporation (974 ) (459 ) (11 ) 1,611 167 Net income (loss) per share attributable to Vicor Corporation: Basic and diluted (0.02 ) (0.01 ) (0.00 ) 0.04 0.00 First Second Third Fourth Total 2016: Net revenues $ 46,027 $ 52,941 $ 53,227 $ 48,085 $ 200,280 Gross margin 19,316 24,471 25,923 21,499 91,209 Consolidated net income (loss) (5,376 ) (550 ) 2,351 (2,686 ) (6,261 ) Net income (loss) attributable to noncontrolling interest (25 ) (6 ) 15 2 (14 ) Net income (loss) attributable to Vicor Corporation (5,351 ) (544 ) 2,336 (2,688 ) (6,247 ) Net income (loss) per share attributable to Vicor Corporation: Basic and diluted (0.14 ) (0.01 ) 0.06 (0.07 ) (0.16 )

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Valuation and Qualifying Accounts	VICOR CORPORATION VALUATION AND QUALIFYING ACCOUNTS Years ended December 31, 2017, 2016, and 2015 Description Balance at Charge (Recovery) Other Charges, Balance at Allowance for doubtful accounts: Year ended: December 31, 2017 $ 153,000 $ 6,000 $ — $ 159,000 December 31, 2016 171,000 (22,000 ) 4,000 153,000 December 31, 2015 183,000 18,000 (30,000 ) 171,000 (1) Reflects uncollectible accounts written off, net of recoveries.

Significant Accounting Polici27

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Principles of consolidation	Principles of consolidation The Consolidated Financial Statements include the accounts of the Company and its subsidiaries. All intercompany transactions and balances have been eliminated upon consolidation. One of the Company’s subsidiaries was not majority owned by the Company prior to 2016, and a second was not majority owned prior to March 31, 2016. Prior to the transactions described in Note 9, these entities were consolidated by the Company as management believed that the Company had the ability to exercise control over their activities and operations.
Use of estimates	Use of estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingencies at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Such estimates and assumptions relate to the useful lives of fixed assets and identified intangible assets, recoverability of long-lived assets, fair value of long-term investments, allowances for doubtful accounts, the net realizable value of inventory, potential reserves relating to litigation matters, accrued liabilities, accrued taxes, deferred tax valuation allowances, assumptions pertaining to share-based payments, and other reserves. Actual results could differ from those based on these estimates and assumptions, and such differences may be material to the financial statements.
Revenue recognition	Revenue recognition Product revenue is recognized in the period when persuasive evidence of an arrangement with a customer exists, the products are shipped and title has transferred to the customer, the price is fixed or determinable, and collection is considered probable. The Company defers revenue and the related cost of sales on shipments to stocking distributors until the distributors resell the products to their customers. The agreements with these stocking distributors allow them to receive price adjustment credits or to return qualifying products for credit, as determined by the Company, in order to reduce the amounts of slow-moving, discontinued, or obsolete product from their inventory. These stocking distributors are also granted price adjustment credits in the event of a price decrease subsequent to the date the product was shipped and invoiced to the stocking distributor. Given the uncertainties associated with the levels of price adjustment credits to be granted to stocking distributors, the sales price to the stocking distributor is not fixed or determinable until the stocking distributor resells the products to its customers. Therefore, the Company defers revenue and the related cost of sales on shipments to stocking distributors until the stocking distributors resell the products to their customers. Accordingly, the Company’s revenue fully reflects end-customer end-customers. The Company evaluates revenue arrangements with potential multi-element deliverables to determine if there is more than one unit of accounting. A deliverable constitutes a separate unit of accounting when it has standalone value and there are no customer-negotiated refund or return rights for the undelivered elements. The Company enters into arrangements containing multiple elements that may include a combination of non-recurring License fees are recognized as earned. The Company recognizes revenue on such arrangements only when the contract is signed, the license term has begun, all obligations have been delivered to the customer, and collection is probable.
Foreign currency translation	Foreign currency translation The financial statements of Vicor Japan Company, Ltd. (“VJCL”), a majority-owned subsidiary, for which the functional currency is the Japanese Yen, have been translated into U.S. Dollars using the exchange rate in effect at the balance sheet date for balance sheet amounts and the average exchange rates in effect during the year for income statement amounts. The gains and losses resulting from the changes in exchange rates from year to year have been reported in other comprehensive income. Transaction gains and losses resulting from the remeasurement of foreign currency denominated assets and liabilities of the Company’s foreign subsidiaries where the functional currency is the U.S. Dollar are included in other income (expense), net. Foreign currency gains (losses) included in other income (expense), net, were approximately $323,000, $(268,000), and $(161,000) in 2017, 2016, and 2015, respectively.
Cash and cash equivalents	Cash and cash equivalents Cash and cash equivalents include funds held in disbursement (i.e., checking) and money market accounts, certificates of deposit, and debt securities with maturities of less than three months at the time of purchase. Cash and cash equivalents are valued at cost, approximating market value. The Company’s money market securities, which are classified as cash equivalents on the balance sheet, are purchased and redeemed at par value. Their estimated fair value is equal to their cost, and, due to the nature of the securities and their classification as cash equivalents, there are no unrealized gains or losses recorded at the balance sheet dates.
Long-term investments	Long-term investments The Company’s principal sources of liquidity are its existing balances of cash and cash equivalents, as well as cash generated from operations. Consistent with the guidelines of the Company’s investment policy, the Company can invest, and has historically invested, its cash balances in demand deposit accounts, money market funds, and auction rate securities meeting certain quality criteria. All of the Company’s investments are subject to credit, liquidity, market, and interest rate risk. The Company’s long-term investments are classified as available-for-sale Available-for-sale non-credit The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity, the net amount of which, along with interest and realized gains and losses, is included in “Other income (expense), net” in the Consolidated Statements of Operations. The Company periodically evaluates investments to determine if impairment is required, whether an impairment is other than temporary, and the measurement of an impairment loss. The Company considers a variety of impairment indicators such as, but not limited to, a significant deterioration in the earnings performance, credit rating, or asset quality of the investment.
Fair value measurements	Fair value measurements The Company accounts for certain financial assets at fair value, defined as the price that would be received to sell an asset or paid to transfer a liability (i.e., an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. A three-level hierarchy is used to show the extent and level of judgment used to estimate fair value measurements: Level 1 Inputs used to measure fair value are unadjusted quoted prices available in active markets for the identical assets or liabilities as of the reporting date. Level 2 Inputs used to measure fair value, other than quoted prices included in Level 1, are either directly or indirectly observable as of the reporting date through correlation with market data, including quoted prices for similar assets and liabilities in active markets and quoted prices in inactive markets. Level 2 also includes assets and liabilities valued using models or other pricing methodologies that do not require significant judgment since the input assumptions used in the models, such as interest rates and volatility factors, are corroborated by readily observable data from actively quoted markets for substantially the full term of the financial instrument. Level 3 Inputs used to measure fair value are unobservable inputs supported by little or no market activity and reflect the use of significant management judgment. These values are generally determined using pricing models for which the assumptions utilize management’s estimates of market participant assumptions. The carrying amounts of cash and cash equivalents, accounts receivable and accounts payable approximate fair value because of the short maturity of these financial instruments.
Allowance for doubtful accounts	Allowance for doubtful accounts The Company maintains allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments, based on assessments of customers’ credit-risk profiles and payment histories. If the financial condition of the Company’s customers were to deteriorate, resulting in an impairment of their ability to make payments, additional allowances may be required. The Company does not require collateral from its customers, although there have been circumstances when the Company has required cash in advance (i.e., a partial down-payment) to facilitate orders in excess of a customer’s established credit limit. To date, such amounts have not been material.
Inventories	Inventories Inventories are valued at the lower of cost (determined using the first-in, first-out The Company provides reserves for inventories estimated to be excess, obsolete, or unmarketable. The Company’s estimation process for assessing net realizable value is based upon its known backlog, projected future demand, historical consumption and expected market conditions. If the Company’s estimated demand and/or market expectations were to change or if product sales were to decline, the Company’s estimation process may cause larger inventory reserves to be recorded, resulting in larger charges to cost of revenues.
Concentrations of risk	Concentrations of risk Financial instruments potentially subjecting the Company to significant concentrations of credit risk consist principally of cash and cash equivalents, of which a significant portion is held by one financial institution, long-term investments, and trade accounts receivable. The Company maintains cash and cash equivalents and certain other financial instruments with various large financial institutions. Generally, amounts invested with these financial institutions are in excess of federal deposit insurance limits. The Company has not experienced any losses in such accounts, and management believes the Company is not exposed to significant credit risk. The Company’s long-term investments consist of highly rated (Aaa/AA+) municipal and corporate debt securities which, as of December 31, 2017, consist of a single auction rate security with a par value of $3,000,000, which is collateralized by student loans. Through December 31, 2017, auctions held for the Company’s auction rate security have failed. The funds associated with an auction rate security that has failed auction may not be accessible until a successful auction occurs, a buyer is found outside of the auction process, the security is called, or the underlying securities have matured. If the credit rating of the issuer of the auction rate security held deteriorates, the Company may be required to adjust the carrying value of the investment for an other-than-temporary decline in value through an impairment charge. The Company’s investment policy, approved by the Board of Directors, limits the amount the Company may invest in any issuer, thereby reducing credit risk concentrations. The Company’s products are sold worldwide to customers ranging from smaller, independent manufacturers of highly specialized electronic devices, to larger OEMs and their contract manufacturers. The Company’s Brick Business Unit (“BBU”) has customers concentrated in aerospace and aviation, defense electronics, industrial automation and equipment, medical diagnostics, rail transportation, and test and measurement instrumentation. The Company’s VI Chip and Picor subsidiaries have customers concentrated in the datacenter and supercomputer segments of the computing market, although they also target applications in aerospace and aviation, defense electronics, networking equipment, solid state lighting, test and measurement instrumentation, and transportation (electric and hybrid vehicles and autonomous vehicles). While, overall, the Company has a broad customer base and sells into a variety of industries, VI Chip and Picor have derived a substantial portion of their revenue from a limited number of customers. This concentration of revenue is a reflection of the relatively early stage of adoption of the technologies, architectures and products offered by these subsidiaries, and their targeting of market leading innovators as initial customers. Concentrations of credit risk with respect to trade accounts receivable are limited due to the number of entities comprising the Company’s customer base. As of December 31, 2017 and 2016, one customer accounted for approximately 17.5% and 14.2%, respectively, of trade account receivables. Components and materials used in the Company’s products are purchased from a variety of vendors. While most of the components are available from multiple sources, some key components for certain VI Chip and Picor products, in particular, are supplied by single vendors. In instances of single source items, the Company maintains levels of inventories management considers appropriate to enable meeting the delivery requirements of customers. If suppliers or subcontractors cannot provide their products or services on time or to the required specifications, the Company may not be able to meet the demand for its products and its delivery times may be negatively affected.
Long-lived assets	Long-lived assets The Company reviews property, plant and equipment and finite-lived intangible assets for impairment whenever events or changes in circumstances indicate the carrying value of such assets may not be recoverable. Management determines whether the carrying value of an asset or asset group is recoverable based on comparison to the undiscounted expected future cash flows the assets are expected to generate over their remaining economic lives. If an asset value is not recoverable, the impairment loss is equal to the amount by which the carrying value of the asset exceeds its fair value, which is determined by either a quoted market price, if any, or a value determined by utilizing a discounted cash flow technique. Evaluation of impairment of long-lived assets requires estimates of future operating results that are used in the preparation of the expected future undiscounted cash flows. Actual future operating results and the remaining economic lives of our long-lived assets could differ from the estimates used in assessing the recoverability of these assets. These differences could result in impairment charges, which could be material.
Intangible assets	Intangible assets Values assigned to patents are amortized using the straight-line method over periods ranging from three to 20 years. Patents and other intangible assets are included in “Other assets” in the accompanying Consolidated Balance Sheets.
Advertising expense	Advertising expense The cost of advertising is expensed as incurred. The Company incurred $2,150,000, $1,818,000, and $1,762,000 in advertising costs during 2017, 2016 and 2015, respectively.
Product warranties	Product warranties The Company generally offers a two-year
Legal Costs	Legal Costs Legal costs in connection with litigation are expensed as incurred.
Net income (loss) per common share	Net income (loss) per common share The Company computes basic net income (loss) per share using the weighted average number of common shares outstanding and diluted net income (loss) per share using the weighted average number of common shares outstanding plus the effect of outstanding dilutive stock options, if any. The following table sets forth the computation of basic and diluted net income (loss) per share for the years ended December 31 (in thousands, except per share amounts): 2017 2016 2015 Numerator: Net income (loss) attributable to Vicor Corporation $ 167 $ (6,247 ) $ 4,927 Denominator: Denominator for basic net income (loss) per share-weighted average shares (1) 39,228 38,842 38,754 Effect of dilutive securities: Employee stock options (2) 705 — 392 Denominator for diluted net income (loss) per share — adjusted weighted-average shares and assumed conversions (3) 39,933 38,842 39,146 Basic net income (loss) per share $ 0.00 $ (0.16 ) $ 0.13 Diluted net income (loss) per share $ 0.00 $ (0.16 ) $ 0.13 (1) Denominator represents weighted average number of Common Shares and Class B Common Shares outstanding. (2) Options to purchase 53,913, 1,696,222 and 238,792 shares of Common Stock in 2017, 2016, and 2015, respectively, were not included in the calculation of net income (loss) per share as the effect would have been antidilutive. (3) Denominator represents weighted average number of Common Shares and Class B Common Shares outstanding for the year, adjusted to include the dilutive effect, if any, of outstanding options.
Income taxes	Income taxes Deferred tax assets and liabilities are determined based on the differences between financial reporting and tax bases of assets and liabilities and are measured using the enacted income tax rates and laws expected to be in effect when the temporary differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance if management determines it is more likely than not that some portion or all of the deferred tax assets will not be realized. All deferred tax assets and liabilities are classified as noncurrent. The Company follows a two-step “more-likely-than-not” “more-likely-than-not”
Stock-based compensation	Stock-based compensation The Company uses the Black-Scholes option-pricing model to calculate the fair value of stock option awards, whether they possess time-based vesting provisions or performance-based vesting provisions, and options granted under the Company’s Employee Stock Purchase Plan, as of their grant date. For stock options with time-based vesting provisions, the calculated compensation expense, net of expected forfeitures, is recognized on a straight-line basis over the service period of the award, which is generally five years for stock options. For stock options with performance-based vesting provisions, recognition of compensation expense, net of expected forfeitures, commences if and when the achievement of the performance criteria is deemed probable. For stock options with performance-based vesting provisions, compensation expense, net of expected forfeitures, when recognized, is recognized over the relevant performance period.
Comprehensive income (loss)	Comprehensive income (loss) The components of comprehensive income (loss) include, in addition to net income (loss), unrealized gains and losses on investments, net of tax and foreign currency translation adjustments related to VJCL, net of tax.
Impact of recently issued accounting standards	Impact of recently issued accounting standards In May 2017, the Financial Accounting Standards Board (“FASB”) issued guidance about which changes to the terms or conditions of a stock-based payment award require an entity to apply modification accounting in Topic 718, Compensation — Stock Compensation In August 2016, the FASB issued guidance to clarify how certain cash receipts and cash payments should be presented in the statement of cash flows. These include debt prepayment, settlement of zero-coupon In June 2016, the FASB issued new guidance which will require measurement and recognition of expected credit losses on certain types of financial instruments. It also modifies the impairment model for available-for-sale In March 2016, the FASB issued new guidance for employee stock-based payment accounting, which makes several modifications to existing guidance related to the accounting for forfeitures, employer tax withholding on stock-based compensation and the financial statement presentation of excess tax benefits or deficiencies. This new guidance also clarifies the statement of cash flows presentation for certain components of stock-based awards. In terms of the accounting for forfeitures, the new guidance allows an option for them to either be estimated, as currently required, or recognized when they occur. The Company will continue to estimate forfeitures. The Company adopted the new standard on January 1, 2017. (See Note 14 – Income Taxes for additional details on the impact of adoption). In February 2016, the FASB issued new guidance for lease accounting, which will require lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. The new guidance establishes a right-of-use In May 2014, the FASB issued new guidance for revenue recognition, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The new guidance, which includes several amendments, replaces most of the prior revenue recognition guidance under U.S. Generally Accepted Accounting Principles (“U.S. GAAP”). The Company’s assessment of the new standard’s impact is substantially complete. The Company will adopt the new guidance as of January 1, 2018 using the modified retrospective method. The most significant impact of the adoption is on the timing of recognition of sales to its stocking distributors. Through December 31, 2017, the Company deferred revenue and the related cost of sales on shipments to stocking distributors until the distributors resold the products to their customers. Upon adoption, the Company is no longer permitted to defer revenue until sale by the stocking distributor to the end customer, but rather, is required to estimate the effects of returns and allowances provided to stocking distributors and record revenue at the time of sale to the stocking distributor. The cumulative effect of adopting this guidance, to be recognized as an increase to the balance of retained earnings as of January 1, 2018, is currently estimated to be approximately $3,300,000. The implementation team’s remaining tasks are to complete documentation for the systems and controls to support the revenue recognition and disclosure requirements under the new standard, and to complete the required disclosures in preparation for filing the Company’s Form 10-Q Other new pronouncements issued but not effective until after December 31, 2017 are not expected to have a material impact on the Company’s consolidated financial statements.

Significant Accounting Polici28

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Computation Of Basic And Diluted Net Income (Loss) Per Share	The following table sets forth the computation of basic and diluted net income (loss) per share for the years ended December 31 (in thousands, except per share amounts): 2017 2016 2015 Numerator: Net income (loss) attributable to Vicor Corporation $ 167 $ (6,247 ) $ 4,927 Denominator: Denominator for basic net income (loss) per share-weighted average shares (1) 39,228 38,842 38,754 Effect of dilutive securities: Employee stock options (2) 705 — 392 Denominator for diluted net income (loss) per share — adjusted weighted-average shares and assumed conversions (3) 39,933 38,842 39,146 Basic net income (loss) per share $ 0.00 $ (0.16 ) $ 0.13 Diluted net income (loss) per share $ 0.00 $ (0.16 ) $ 0.13 (1) Denominator represents weighted average number of Common Shares and Class B Common Shares outstanding. (2) Options to purchase 53,913, 1,696,222 and 238,792 shares of Common Stock in 2017, 2016, and 2015, respectively, were not included in the calculation of net income (loss) per share as the effect would have been antidilutive. (3) Denominator represents weighted average number of Common Shares and Class B Common Shares outstanding for the year, adjusted to include the dilutive effect, if any, of outstanding options.

Stock-Based Compensation and 29

Stock-Based Compensation and Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Stock-Based Compensation Expense	Stock-based compensation expense for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Cost of revenues $ 187 $ 95 $ 230 Selling, general and administrative 1,125 412 1,246 Research and development 423 (1 ) 306 Total stock-based compensation $ 1,735 $ 506 $ 1,782
Summary of Compensation Expense by Type of Award	Compensation expense by type of award for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Stock options $ 1,546 $ 506 $ 1,782 ESPP 189 — — Total stock-based compensation $ 1,735 $ 506 $ 1,782
Weighted-Average Assumptions for Non Performance-Based Fair Value for Stock Options	The fair value for non performance-based stock options awarded for the years shown below was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions: Vicor: 2017 2016 2015 Risk-free interest rate 2.1 % 1.5 % 2.0 % Expected dividend yield — — — Expected volatility 43 % 45 % 51 % Expected lives (years) 7.1 7.2 7.2 VI Chip: 2017 2016 2015 Risk-free interest rate 1.9 % 1.7 % 2.1 % Expected dividend yield — — — Expected volatility 32 % 34 % 37 % Expected lives (years) 6.5 6.5 6.5 Picor: 2017 2016 2015 Risk-free interest rate 1.9 % 1.5 % 1.9 % Expected dividend yield — — — Expected volatility 48 % 42 % 41 % Expected lives (years) 6.5 6.5 6.5
2000 Plan, Vicor [Member]
Stock-Based Compensation Expense	A summary of the activity under the 2000 Plan as of December 31, 2017 and changes during the year then ended, is presented below (in thousands except for share and weighted-average data): Options Weighted- Weighted- Aggregate Outstanding on December 31, 2016 1,696,222 $ 8.82 Granted 96,322 $ 18.41 Forfeited and expired (25,087 ) $ 10.92 Exercised (401,540 ) $ 8.21 Outstanding on December 31, 2017 1,365,917 $ 9.63 6.21 $ 15,409 Exercisable on December 31, 2017 707,244 $ 8.01 5.82 $ 9,116 Vested or expected to vest as of December 31, 2017(1) 1,332,671 $ 9.54 6.19 $ 15,161 (1) In addition to the vested options, the Company expects a portion of the unvested options to vest at some point in the future. The number of options expected to vest is calculated by applying an estimated forfeiture rate to the unvested options.
Picor Plan [Member]
Stock-Based Compensation Expense	A summary of the activity under the 2001 Picor Plan as of December 31, 2017 and changes during the year then ended, is presented below (in thousands except for share and weighted-average data): Options Weighted- Weighted- Aggregate Outstanding on December 31, 2016 9,530,987 $ 0.62 Granted 673,000 $ 0.62 Forfeited and expired (126,000 ) $ 0.73 Exercised (12,000 ) $ 0.41 Outstanding on December 31, 2017 10,065,987 $ 0.62 3.80 $ 493 Exercisable on December 31, 2017 8,384,987 $ 0.61 3.31 $ 400 Vested or expected to vest as of December 31, 2017(1) 9,996,810 $ 0.62 3.78 $ 492 (1) In addition to the vested options, the Company expects a portion of the unvested options to vest at some point in the future. Options expected to vest is calculated by applying an estimated forfeiture rate to the unvested options.
Vi Chip Plan [Member]
Stock-Based Compensation Expense	A summary of the activity under the 2007 VI Chip Plan as of December 31, 2017 and changes during the year then ended, is presented below (in thousands except for share and weighted-average data): Options Weighted- Weighted- Aggregate Outstanding on December 31, 2016 9,933,750 $ 1.00 Granted 9,771,500 $ 0.96 Forfeited and expired (6,613,000 ) $ 1.00 Exercised — $ — Outstanding on December 31, 2017 (1) 13,092,250 $ 0.97 5.78 $ — Exercisable on December 31, 2017 810,700 $ 1.00 4.46 $ — Vested or expected to vest as of December 31, 2017(2) 11,210,701 $ 0.97 5.67 $ — (1) Of the total VI Chip options outstanding on December 31, 2017, 5,500,000 options had been granted to Dr. Vinciarelli, the Company’s Chief Executive Officer. (2) In addition to the vested options, the Company expects a portion of the unvested options to vest at some point in the future. Options expected to vest is calculated by applying an estimated forfeiture rate to the unvested options.

Long-Term Investments (Tables)

Long-Term Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Summary of Available-for-Sale Securities	The following is a summary of available-for-sale December 31, 2017 Cost Gross Gross Estimated Fair Failed Auction Security $ 3,000 $ — $ 475 $ 2,525 December 31, 2016 Cost Gross Gross Estimated Fair Failed Auction Security $ 3,000 $ — $ 492 $ 2,508
Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturities	The amortized cost and estimated fair value of available-for-sale Cost Estimated Fair Due in twenty to forty years $ 3,000 $ 2,525
Rollforward of Credit (Gain) Loss Recognized in Earnings on Available-for-Sale Auction Rate Securities	The following table represents a rollforward of the activity related to the credit loss recognized in earnings on available-for-sale 2017 2016 2015 Balance at the beginning of the period $ 59 $ 72 $ 84 Reductions in the amount related to credit gain for which other-than-temporary impairment was not previously recognized (11 ) (13 ) (12 ) Balance at the end of the period $ 48 $ 59 $ 72

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Fair Value on Recurring Basis	Assets and liabilities measured at fair value on a recurring basis included the following as of December 31, 2017 (in thousands): Using Quoted Prices Significant Significant (Level 3) Total Fair Cash equivalents: Money market funds $ 9,279 $ — $ — $ 9,279 Long-term investments: Failed Auction Security — — 2,525 2,525 Liabilities: Contingent consideration obligations — — (678 ) (678 ) Assets measured at fair value on a recurring basis included the following as of December 31, 2016 (in thousands): Using Quoted Prices Significant Significant Total Fair Cash equivalents: Money market funds $ 10,114 $ — $ — $ 10,114 Long-term investments: Failed Auction Security — — 2,508 2,508 Liabilities: Contingent consideration obligation — — (253 ) (253 )
Quantitative Information about Level 3 Fair Value Measurements	Quantitative information about Level 3 fair value measurements as of December 31, 2017 are as follows (dollars in thousands): Fair Valuation Unobservable Input Weighted Failed Auction Security $ 2,525 Discounted Cumulative probability of earning the maximum rate until maturity 0.06 % Cumulative probability of principal return prior to maturity 93.71 % Cumulative probability of default 6.24 % Liquidity risk premium 5.00 % Recovery rate in default 40.00 %
Change in Estimated Fair Values Calculated for Investment Valued on Recurring Basis Utilizing Level 3 Inputs	The change in the estimated fair value calculated for the investment valued on a recurring basis utilizing Level 3 inputs (i.e., the Failed Auction Security) for the year ended December 31, 2017 was as follows (in thousands): Balance at the beginning of the period $ 2,508 Credit gain on available-for-sale 11 Gain included in Other comprehensive income (loss) 6 Balance at the end of the period $ 2,525
Change in Estimated Fair Value Calculated for Liabilities Valued on Recurring Basis Utilizing Level 3 Inputs	The change in the estimated fair value calculated for the liabilities valued on a recurring basis utilizing Level 3 inputs (i.e., the Contingent consideration obligations) for the year ended December 31, 2017 was as follows (in thousands): Balance at the beginning of the period $ 253 Increase in estimated contingent consideration obligations (see Note 9) 650 Payments (225 ) Balance at the end of the period $ 678

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Summary of Inventories	Inventories as of December 31 were as follows (in thousands): 2017 2016 Raw materials $ 27,400 $ 18,648 Work-in-process 3,596 3,361 Finished goods 5,503 5,127 Net balance $ 36,499 $ 27,136

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, plant and equipment as of December 31 were as follows (in thousands): 2017 2016 Land $ 2,089 $ 2,089 Buildings and improvements 45,147 43,950 Machinery and equipment 243,392 237,434 Furniture and fixtures 6,320 5,656 Construction in-progress 4,120 2,471 301,068 291,600 Accumulated depreciation and amortization (259,712 ) (254,026 ) Net balance $ 41,356 $ 37,574

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Patents [Member]
Schedule of Patent Cost and Other Asset	Patent costs, which are included in other assets in the accompanying Consolidated Balance Sheets, as of December 31 were as follows (in thousands): 2017 2016 Patent costs $ 2,093 $ 2,427 Accumulated amortization (1,386 ) (1,598 ) $ 707 $ 829

Product Warranties (Tables)

Product Warranties (Tables)	12 Months Ended
	Dec. 31, 2017
Guarantees and Product Warranties [Abstract]
Product Warranty Activity	Product warranty activity for the years ended December 31 was as follows (in thousands): 2017 2016 2015 Balance at the beginning of the period $ 214 $ 585 $ 204 Accruals for warranties for products sold in the period 346 358 715 Fulfillment of warranty obligations (194 ) (527 ) (334 ) Revisions of estimated obligations (76 ) (202 ) — Balance at the end of the period $ 290 $ 214 $ 585

Other Income (Expense), Net (Ta

Other Income (Expense), Net (Tables)	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Components of Other Income	The major changes in the components of Other income (expense), net for the years ended December 31 were as follows (in thousands): 2017 2016 2015 Rental income $ 792 $ 462 $ — Foreign currency gains (losses), net 323 (268 ) (161 ) Interest income 124 68 47 Gain (loss) on disposal of equipment 14 (4 ) 60 Credit gains on available-for-sale 11 13 12 Other (2 ) 13 67 $ 1,262 $ 284 $ 25

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Reconciliation of Federal Statutory Rate on Loss before Income Taxes and before Gain from Sale of Equity Method Investment Rate to Effective Income Tax Rate	The reconciliation of the federal statutory rate on the loss before income taxes and before the gain from sale of equity method investment to the effective income tax rate for the years ended December 31 is as follows: 2017 2016 2015 Statutory federal tax rate (34.0 )% (34.0 )% (34.0 )% State income taxes, net of federal income tax benefit 97.2 1.9 46.4 Rate change due to tax reform 3,441.1 — — Tax credits (1,222.3 ) (13.6 ) 29.9 Increase (decrease) in valuation allowance (936.1 ) 46.5 (138.4 ) Permanent items (861.2 ) 0.9 21.2 Refundable income taxes — AMT credit (751.0 ) — — Foreign rate differential and deferred items (91.8 ) (0.8 ) (18.2 ) Decrease in tax reserves (5.1 ) — (248.6 ) Capital gain on sale to noncontrolling interest — 3.9 237.8 Decrease in unremitted Vicor Custom Power earnings — (0.9 ) (108.7 ) Book income attributable to noncontrolling interest — 0.1 47.0 Other (0.1 ) (0.2 ) (0.1 ) (363.3 )% 3.8 % (165.7 )%
Schedule of Domestic and Foreign Components of Income (Loss) Before Income Taxes and before the Gain from Sale of Equity Method Investment	For financial reporting purposes, income (loss) before income taxes and before the gain from sale of equity method investment for the years ended December 31 include the following components (in thousands): 2017 2016 2015 Domestic $ (1,591 ) $ (6,034 ) $ 1,373 Foreign 1,493 4 (1,615 ) $ (98 ) $ (6,030 ) $ (242 )
Schedule of Components of Provision (Benefit) for Income Taxes	Significant components of the provision (benefit) for income taxes for the years ended December 31 are as follows (in thousands): 2017 2016 2015 Current: Federal $ (736 ) $ — $ 144 State 156 172 (473 ) Foreign 396 137 111 (184 ) 309 (218 ) Deferred: Federal — (55 ) (274 ) Foreign (172 ) (23 ) 91 (172 ) (78 ) (183 ) $ (356 ) $ 231 $ (401 )
Schedule of Significant Components of Deferred Tax Assets and Liabilities	Significant components of the Company’s deferred tax assets and liabilities as of December 31 were as follows (in thousands): 2017 2016 Deferred tax assets: Research and development tax credit carryforwards $ 20,019 $ 13,967 Net operating loss carryforwards 4,918 4,902 Stock-based compensation 2,793 4,066 Investment tax credit carryforwards 2,181 1,576 Inventory reserves 2,059 3,143 Vacation accrual 1,255 1,928 Contingent consideration liabilities 148 — Unrealized loss on investments 135 136 Deferred revenue 79 154 Warranty reserves 45 73 Bad debt reserves 36 52 Alternative minimum tax credit carryforward — 340 Other 273 331 Total deferred tax assets 33,941 30,668 Less: Valuation allowance for deferred tax assets (33,024 ) (29,274 ) Net deferred tax assets 917 1,394 Deferred tax liabilities: Prepaid expenses (470 ) (654 ) Patent amortization (161 ) (296 ) Depreciation (76 ) (406 ) Total deferred tax liabilities (707 ) (1,356 ) Net deferred tax assets (liabilities) $ 210 $ 38
Schedule of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): 2017 2016 2015 Balance on January 1 $ 946 $ 830 $ 1,254 Additions based on tax positions related to the current year 138 125 120 Additions for tax positions of prior years 29 — — Settlements (1 ) — (480 ) Lapse of statute (8 ) (9 ) (64 ) Balance on December 31 $ 1,104 $ 946 $ 830

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Summary of Future Minimum Rental Commitments under Non-Cancelable Operating Leases	The Company leases certain of its office and manufacturing space. The future minimum rental commitments under non-cancelable Year 2018 $ 1,742 2019 1,152 2020 872 2021 467 2022 and thereafter 1,002

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Significant Segment Financial Data	The following table provides significant segment financial data as of and for the years ended December 31 (in thousands): BBU VI Chip Picor Corporate Eliminations Total (1) 2017: Net revenues $ 151,789 $ 61,330 $ 26,297 $ — $ (11,586 ) $ 227,830 Income (loss) from operations 5,615 (11,495 ) 5,400 (880 ) — (1,360 ) Total assets 232,255 34,809 13,509 59,550 (174,399 ) 165,724 Depreciation and amortization 3,907 2,782 747 1,457 — 8,893 2016: Net revenues $ 151,428 $ 39,947 $ 16,684 $ — $ (7,779 ) $ 200,280 Income (loss) from operations 11,750 (16,494 ) (637 ) (933 ) — (6,314 ) Total assets 196,987 21,389 8,583 73,253 (146,145 ) 154,067 Depreciation and amortization 4,258 2,235 545 1,400 — 8,438 2015: Net revenues $ 173,064 $ 36,688 $ 17,304 $ — $ (6,862 ) $ 220,194 Income (loss) from operations 21,743 (21,040 ) (290 ) (680 ) — (267 ) Total assets 170,939 15,577 5,369 81,824 (116,164 ) 157,545 Depreciation and amortization 4,538 2,740 442 1,422 — 9,142 (1) The elimination for net revenues is principally related to inter-segment revenues of Picor to BBU and VI Chip and for inter-segment revenues of VI Chip to BBU. The elimination for total assets is principally related to inter-segment accounts receivable due to BBU for the funding of VI Chip and Picor operations.
Schedule of Net Revenues from Unaffiliated Customers by Country Based on the Location of the Customer	Net revenues from unaffiliated customers by country, based on the location of the customer, for the years ended December 31 were as follows (in thousands): 2017 2016 2015 United States $ 83,871 $ 80,603 $ 88,136 Europe 24,078 22,495 29,686 Asia Pacific 114,365 91,848 94,845 All other 5,516 5,334 7,527 $227,830 $200,280 $220,194

Quarterly Results of Operatio40

Quarterly Results of Operations (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Summary of Unaudited Quarterly Financial Data	The following table sets forth certain unaudited quarterly financial data for the years ended December 31 (in thousands, except per share amounts): First Second Third Fourth Total 2017: Net revenues $ 54,462 $ 57,709 $ 56,888 $ 58,771 $ 227,830 Gross margin 23,652 25,930 25,143 26,931 101,656 Consolidated net income (loss) (954 ) (445 ) 38 1,619 258 Net income attributable to noncontrolling interest 20 14 49 8 91 Net income (loss) attributable to Vicor Corporation (974 ) (459 ) (11 ) 1,611 167 Net income (loss) per share attributable to Vicor Corporation: Basic and diluted (0.02 ) (0.01 ) (0.00 ) 0.04 0.00 First Second Third Fourth Total 2016: Net revenues $ 46,027 $ 52,941 $ 53,227 $ 48,085 $ 200,280 Gross margin 19,316 24,471 25,923 21,499 91,209 Consolidated net income (loss) (5,376 ) (550 ) 2,351 (2,686 ) (6,261 ) Net income (loss) attributable to noncontrolling interest (25 ) (6 ) 15 2 (14 ) Net income (loss) attributable to Vicor Corporation (5,351 ) (544 ) 2,336 (2,688 ) (6,247 ) Net income (loss) per share attributable to Vicor Corporation: Basic and diluted (0.14 ) (0.01 ) 0.06 (0.07 ) (0.16 )

Significant Accounting Polici41

Significant Accounting Policies - Additional Information (Detail)	Jan. 01, 2017	Dec. 31, 2017USD ($)Customer	Dec. 31, 2016USD ($)Customer	Dec. 31, 2015USD ($)
Revenue, Major Customer [Line Items]
Gross deferred revenue		$ 4,659,000	$ 3,337,000
Gross deferred cost of revenue		$ 2,135,000	$ 1,445,000
Revenue recognized under multi-element		3.00%	3.00%	3.00%
Foreign currency gains (losses)		$ 323,000	$ (268,000)	$ (161,000)
Maturity period of cash and cash equivalents			Less than three months
Available-for-sale securities, failed auction, value		$ 3,000,000
Number of customers accounted for trade account receivable | Customer		1	1
Cost of advertising		$ 2,150,000	$ 1,818,000	$ 1,762,000
Product warranty period		2 years
Percentage likelihood of tax benefit settlement		50.00%
Recognition period of non performance based stock options		5 years
Military Grade Products [Member]
Revenue, Major Customer [Line Items]
Extended warranty period	3 years
Customer One [Member]
Revenue, Major Customer [Line Items]
Percentage of trade account receivable		17.50%	14.20%
Maximum [Member]
Revenue, Major Customer [Line Items]
Recognition period		12 months
Estimated useful life of intangible assets		20 years
Minimum [Member]
Revenue, Major Customer [Line Items]
Recognition period		6 months
Estimated useful life of intangible assets		3 years

Significant Accounting Polici42

Significant Accounting Policies - Computation Of Basic And Diluted Net Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income (loss) attributable to Vicor Corporation	$ 1,611	$ (11)	$ (459)	$ (974)	$ (2,688)	$ 2,336	$ (544)	$ (5,351)	$ 167	$ (6,247)	$ 4,927
Denominator:
Denominator for basic net income (loss) per share-weighted average shares									39,228	38,842	38,754
Effect of dilutive securities:
Employee stock options									705		392
Denominator for diluted net income (loss) per share - adjusted weighted-average shares and assumed conversions									39,933	38,842	39,146
Basic net income (loss) per share									$ 0	$ (0.16)	$ 0.13
Diluted net income (loss) per share									$ 0	$ (0.16)	$ 0.13

Significant Accounting Polici43

Significant Accounting Policies - Computation Of Basic And Diluted Net Income (Loss) Per Share (Parenthetical) (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Options to purchase shares of Common Stock not included in the computation of diluted income (loss) per share	53,913	1,696,222	238,792

Stock-Based Compensation and 44

Stock-Based Compensation and Employee Benefit Plans - Additional Information (Detail) - USD ($)	Nov. 11, 2011	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of Option			10 years
Employee's compensation plan			The Company matches employee contributions to the plan at a rate of 50%, up to the first 3% of an employee's compensation.
Employee contributions			20.00%
Company contribution to the plan			$ 937,000	$ 882,000	$ 854,000
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employees pre-tax salary			1.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employees pre-tax salary			80.00%
Picor Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-qualified stock options			10,065,987	9,530,987
Stock options, grants in period			673,000
Maturity period of US Treasury Bond			7 years
Chip options actually vest forfeiture			93.00%	92.00%	93.00%
Annual forfeiture rate			2.50%	2.50%	2.50%
Share exercisable			8,384,987	7,915,219	8,053,490
Weighted average exercise prices			$ 0.61	$ 0.62	$ 0.64
Total Intrinsic value			$ 3,000	$ 24,000	$ 72,000
Options Exercised			5,000	17,000	14,000
Fair value of stock options that vested			180,000	$ 155,000	$ 39,000
Total unrecognized compensation cost			$ 322,000
Compensation cost recognized over a weighted-average period			3 years 1 month 6 days
Expected recognized expenses, Year One			$ 117,000
Expected recognized expenses, Year Two			83,000
Expected recognized expenses, Year Three			61,000
Expected recognized expenses, Year Four			45,000
Expected recognized expenses, Year Five			$ 16,000
Weighted-average fair value			$ 0.27	$ 0.26	$ 0.48
Vi Chip Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-qualified stock options			13,092,250	9,933,750
Stock options, grants in period			9,771,500
Maturity period of US Treasury Bond			7 years
Chip options actually vest forfeiture			76.00%	76.00%	78.00%
Annual forfeiture rate			9.00%	9.00%	8.50%
Share exercisable			810,700	7,074,650	7,042,600
Weighted average exercise prices			$ 1	$ 1	$ 1
Total Intrinsic value					$ 0
Options Exercised			$ 0	$ 0	1,000
Fair value of stock options that vested			2,900,000	$ 0	$ 1,000
Total unrecognized compensation cost			$ 2,395,000
Compensation cost recognized over a weighted-average period			4 years
Expected recognized expenses, Year One			$ 603,000
Expected recognized expenses, Year Two			544,000
Expected recognized expenses, Year Three			503,000
Expected recognized expenses, Year Four			483,000
Expected recognized expenses, Year Five			$ 262,000
Weighted-average fair value			$ 0.29	$ 0.01	$ 0.01
2000 Plan, Vicor [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock reserved for issuance			10,000,000
Non-qualified stock options granted to non-employees			85.00%
Non-qualified stock options			1,365,917	1,696,222
Stock options, grants in period			96,322
Chip options actually vest forfeiture			85.00%	86.00%	88.00%
Annual forfeiture rate			5.25%	5.00%	4.25%
Share exercisable			707,244	730,388	565,861
Weighted average exercise prices			$ 8.01	$ 7.74	$ 7.24
Total Intrinsic value			$ 4,395,000	$ 1,392,000	$ 928,000
Options Exercised			3,295,000	1,572,000	805,000
Fair value of stock options that vested			774,000	$ 365,000	$ 1,194,000
Total unrecognized compensation cost			$ 920,000
Compensation cost recognized over a weighted-average period			1 year 4 months 24 days
Expected recognized expenses, Year One			$ 488,000
Expected recognized expenses, Year Two			249,000
Expected recognized expenses, Year Three			116,000
Expected recognized expenses, Year Four			52,000
Expected recognized expenses, Year Five			$ 15,000
Weighted-average fair value			$ 8.71	$ 4.94	$ 6.76
Stock Bonus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock purchase by non-employees			109,964
2001 Picor Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock reserved for issuance			20,000,000
Non-qualified stock options			0
2007 VI Chip Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock reserved for issuance			14,000,000
Non-qualified stock options			0			2,984,250
Stock options, grants in period	0
Stock-based compensation expense reversed		$ 768,000
2007 VI Chip Plan [Member] | Cost of Revenues [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Decrease in costs and expenses due to reversal of share-based compensation expense		86,000
2007 VI Chip Plan [Member] | Selling, General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Decrease in costs and expenses due to reversal of share-based compensation expense		516,000
2007 VI Chip Plan [Member] | Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Decrease in costs and expenses due to reversal of share-based compensation expense		$ 166,000
2017 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-qualified stock options granted to non-employees			85.00%
Maximum number of shares authorized for issuances			2,000,000
Maximum percentage of payroll deductions on employee's compensation			15.00%
Offering period of employee stock purchase plan			6 months

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 1,735	$ 506	$ 1,782
Cost of Revenues [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	187	95	230
Selling, General and Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	1,125	412	1,246
Research and Development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 423	$ (1)	$ 306

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Compensation Expense by Type of Award (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 1,735	$ 506	$ 1,782
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	1,546	$ 506	$ 1,782
ESPP [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 189

Stock-Based Compensation and 47

Stock-Based Compensation and Employee Benefit Plans - Weighted-Average Assumptions for Non Performance-Based Fair Value for Stock Options (Detail) - Non Performance-Based Stock Options [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Vicor [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Risk-free interest rate	2.10%	1.50%	2.00%
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility	43.00%	45.00%	51.00%
Expected lives (years)	7 years 1 month 6 days	7 years 2 months 12 days	7 years 2 months 12 days
VI Chip [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Risk-free interest rate	1.90%	1.70%	2.10%
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility	32.00%	34.00%	37.00%
Expected lives (years)	6 years 6 months	6 years 6 months	6 years 6 months
Picor [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Risk-free interest rate	1.90%	1.50%	1.90%
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility	48.00%	42.00%	41.00%
Expected lives (years)	6 years 6 months	6 years 6 months	6 years 6 months

Stock-Based Compensation and 48

Stock-Based Compensation and Employee Benefit Plans - Summary of the Activity under the 2000 Plan (Detail) - 2000 Plan, Vicor [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Options Outstanding, Beginning balance	1,696,222
Options Outstanding, Granted	96,322
Options Outstanding, Forfeited and expired	(25,087)
Options Outstanding, Exercised	(401,540)
Options Outstanding, Ending balance	1,365,917
Options Outstanding, Exercisable	707,244	730,388	565,861
Options Outstanding, Vested or expected to vest	1,332,671
Weighted Average Exercise Price, Beginning balance	$ 8.82
Weighted Average Exercise Price, Granted	18.41
Weighted Average Exercise Price, Forfeited and expired	10.92
Weighted Average Exercise Price, Exercised	8.21
Weighted Average Exercise Price, Ending balance	9.63
Weighted Average Exercise Price, Exercisable	8.01	$ 7.74	$ 7.24
Weighted Average Exercise Price, Vested or expected to vest	$ 9.54
Weighted-Average Remaining Contractual Life in Years, Outstanding	6 years 2 months 16 days
Weighted-Average Remaining Contractual Life in Years, Exercisable	5 years 9 months 25 days
Weighted-Average Remaining Contractual Life in Years, Vested or expected to vest	6 years 2 months 8 days
Aggregate Intrinsic Value, Outstanding	$ 15,409
Aggregate Intrinsic Value, Exercisable	9,116
Aggregate Intrinsic Value, Vested or expected to vest	$ 15,161

Stock-Based Compensation and 49

Stock-Based Compensation and Employee Benefit Plans - Summary of the Activity under the Picor Stock Option Plans (Detail) - Picor Plan [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Options Outstanding, Beginning balance	9,530,987
Options Outstanding, Granted	673,000
Options Outstanding, Forfeited and expired	(126,000)
Options Outstanding, Exercised	(12,000)
Options Outstanding, Ending balance	10,065,987
Options Outstanding, Exercisable	8,384,987	7,915,219	8,053,490
Options Outstanding, Vested or expected to vest	9,996,810
Weighted Average Exercise Price, Beginning balance	$ 0.62
Weighted Average Exercise Price, Granted	0.62
Weighted Average Exercise Price, Forfeited and expired	0.73
Weighted Average Exercise Price, Exercised	0.41
Weighted Average Exercise Price, Ending balance	0.62
Weighted Average Exercise Price, Exercisable	0.61	$ 0.62	$ 0.64
Weighted Average Exercise Price, Vested or expected to vest	$ 0.62
Weighted-Average Remaining Contractual Life in Years, Outstanding	3 years 9 months 18 days
Weighted-Average Remaining Contractual Life in Years, Exercisable	3 years 3 months 22 days
Weighted-Average Remaining Contractual Life in Years, Vested or expected to vest	3 years 9 months 11 days
Aggregate Intrinsic Value, Outstanding	$ 493
Aggregate Intrinsic Value, Exercisable	400
Aggregate Intrinsic Value, Vested or expected to vest	$ 492

Stock-Based Compensation and 50

Stock-Based Compensation and Employee Benefit Plans - Summary of the Activity under the VI Chip Stock Option Plans (Detail) - Vi Chip Plan [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Options Outstanding, Beginning balance	9,933,750
Options Outstanding, Granted	9,771,500
Options Outstanding, Forfeited and expired	(6,613,000)
Options Outstanding, Exercised	0
Options Outstanding, Ending balance	13,092,250
Options Outstanding, Exercisable	810,700	7,074,650	7,042,600
Options Outstanding, Vested or expected to vest	11,210,701
Weighted Average Exercise Price, Beginning balance	$ 1
Weighted Average Exercise Price, Granted	0.96
Weighted Average Exercise Price, Forfeited and expired	1
Weighted Average Exercise Price, Exercised	0
Weighted Average Exercise Price, Ending balance	0.97
Weighted Average Exercise Price, Exercisable	1	$ 1	$ 1
Weighted Average Exercise Price, Vested or expected to vest	$ 0.97
Weighted-Average Remaining Contractual Life in Years, Outstanding	5 years 9 months 11 days
Weighted-Average Remaining Contractual Life in Years, Exercisable	4 years 5 months 16 days
Weighted-Average Remaining Contractual Life in Years, Vested or expected to vest	5 years 8 months 2 days
Aggregate Intrinsic Value, Outstanding	$ 0
Aggregate Intrinsic Value, Exercisable	0
Aggregate Intrinsic Value, Vested or expected to vest	$ 0

Stock-Based Compensation and 51

Stock-Based Compensation and Employee Benefit Plans - Summary of the Activity under the VI Chip Stock Option Plans (Parenthetical) (Detail) - Vi Chip Plan [Member]	12 Months Ended
	Dec. 31, 2017shares
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Granted, shares	9,771,500
Chief Executive Officer [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Granted, shares	5,500,000

Long-Term Investments - Additio

Long-Term Investments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Unrealized Losses On Short Term And Long Term Investments [Line Items]
Minimum period for which failed auction securities been in unrealized loss position	12 months
Failed Auction Security [Member]
Unrealized Losses On Short Term And Long Term Investments [Line Items]
Amortized cost of securities	$ 3,000,000	$ 3,000,000
Period for which failed auction securities been in unrealized loss position	Exceeds 12 months
Estimated Fair Value	$ 2,525,000	2,508,000
Gross Unrealized Losses	475,000	492,000
Aggregate credit loss	48,000	$ 59,000	$ 72,000	$ 84,000
Aggregate temporary impairment loss	$ 427,000

Long-Term Investments - Summary

Long-Term Investments - Summary of Available-for-Sale Securities (Detail) - Failed Auction Security [Member] - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 3,000,000	$ 3,000,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	475,000	492,000
Estimated Fair Value	$ 2,525,000	$ 2,508,000

Long-Term Investments - Amortiz

Long-Term Investments - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturities (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Available-for-sale Securities, Debt Maturities [Abstract]
Due in twenty to forty years, Cost	$ 3,000
Due in twenty to forty years, Estimated Fair Value	$ 2,525

Long-Term Investments - Rollfor

Long-Term Investments - Rollforward of Credit (Gain) Loss Recognized in Earnings on Available-for-Sale Auction Rate Securities (Detail) - Failed Auction Security [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Balance at the beginning of the period	$ 59,000	$ 72,000	$ 84,000
Reductions in the amount related to credit gain for which other-than-temporary impairment was not previously recognized	(11,000)	(13,000)	(12,000)
Balance at the end of the period	$ 48,000	$ 59,000	$ 72,000

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Contingent Consideration Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Liabilities, fair value on recurring basis	$ (678,000)	$ (253,000)
Failed Auction Security [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated Fair Value	2,525,000	2,508,000
Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Cash equivalents	9,279,000	10,114,000
Recurring [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Cash equivalents	9,279,000	10,114,000
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Contingent Consideration Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Liabilities, fair value on recurring basis	(678,000)	(253,000)
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Failed Auction Security [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated Fair Value	$ 2,525,000	$ 2,508,000

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017USD ($)
Fair Value Disclosures [Abstract]
Percent of credit loss	2.00%
Rate of return required	5.00%
Estimated timeframe for auctions of securities minimum	3 years
Estimated timeframe for auctions of securities maximum	5 years
Percentage of liquidity risk premium	5.00%
Increase or decrease in the liquidity risk premium	1.00%
Increase or decrease, respectively, the fair value of the Failed Auction Securities	$ 100,000
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	$ 0

Fair Value Measurements - Quant

Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Detail) - Failed Auction Security [Member] - Significant Unobservable Inputs (Level 3) [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 2,525
Valuation Technique	Discounted cash flow
Cumulative Probability of Earning Maximum Rate Until Maturity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable Input	Cumulative probability of earning the maximum rate until maturity
Weighted Average Interest Rate	0.06%
Cumulative Probability of Principal Return Prior to Maturity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable Input	Cumulative probability of principal return prior to maturity
Weighted Average Interest Rate	93.71%
Cumulative Probability of Default [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable Input	Cumulative probability of default
Weighted Average Interest Rate	6.24%
Liquidity Risk Premium [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable Input	Liquidity risk premium
Weighted Average Interest Rate	5.00%
Recovery Rate in Default [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable Input	Recovery rate in default
Weighted Average Interest Rate	40.00%

Fair Value Measurements - Chang

Fair Value Measurements - Change in Estimated Fair Values Calculated for Investment Valued on Recurring Basis Utilizing Level 3 Inputs (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Fair Value Disclosures [Abstract]
Balance at the beginning of the period	$ 2,508
Credit gain on available-for-sale security included in Other income (expense), net	11
Gain included in Other comprehensive income (loss)	6
Balance at the end of the period	$ 2,525

Fair Value Measurements - Cha60

Fair Value Measurements - Change in Estimated Fair Value Calculated for Liabilities Valued on Recurring Basis Utilizing Level 3 Inputs (Detail) - Significant Unobservable Inputs (Level 3) [Member] - Contingent Consideration Obligations [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at the beginning of the period	$ 253
Increase in estimated contingent consideration obligations	650
Payments	(225)
Balance at the end of the period	$ 678

Inventories - Summary of Invent

Inventories - Summary of Inventories (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw materials	$ 27,400	$ 18,648
Work-in-process	3,596	3,361
Finished goods	5,503	5,127
Net balance	$ 36,499	$ 27,136

Property, Plant and Equipment -

Property, Plant and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 30, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 8,763,000	$ 8,304,000	$ 9,028,000
Capital expenditure commitments	$ 1,911,000
Maximum [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization period	39 years
Minimum [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization period	3 years

Property, Plant and Equipment63

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Land	$ 2,089	$ 2,089
Buildings and improvements	45,147	43,950
Machinery and equipment	243,392	237,434
Furniture and fixtures	6,320	5,656
Construction in-progress and deposits	4,120	2,471
Property, plant and equipment, gross, total	301,068	291,600
Accumulated depreciation and amortization	(259,712)	(254,026)
Net balance	$ 41,356	$ 37,574

Other Investments - Additional

Other Investments - Additional Information (Detail)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2015USD ($)	Sep. 30, 2015USD ($)	Dec. 31, 2017USD ($)Agreement	Dec. 31, 2015USD ($)	Dec. 31, 2008USD ($)
Variable Interest Entity [Line Items]
Gain from equity method investment				$ 5,000,000
Great Wall Semiconductor Corporation (GWS) [Member]
Variable Interest Entity [Line Items]
Gross investment			$ 4,999,719		$ 0
Gain from equity method investment	$ 4,999,719		$ 4,999,719
Number of supply agreements with GWS | Agreement			2
Purchase of components under agreement		$ 1,662,000

Noncontrolling Interest Trans65

Noncontrolling Interest Transactions - Additional Information (Detail) - USD ($)	Mar. 30, 2016	Dec. 28, 2015	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2016
Noncontrolling Interest [Line Items]
Contingent consideration				$ 678,000		$ 253,000
Noncontrolling interest					$ 0
Reduction in cash, short-term interest receivable, and long-term investments					1,742,000
Deconsolidation effect in statement of operations					$ 28,000
Noncontrolling interest				$ 305,000		$ 208,000
Royalty payment description				Through June 30, 2021
Aegis Power Systems Inc [Member]
Noncontrolling Interest [Line Items]
Minority interest percentage by non controlling interest		49.00%			49.00%
Minority interest percentage by parent		51.00%
Noncontrolling interest		$ 1,698,000
Deconsolidated cash					$ 2,090,000
Deconsolidated other net assets					1,317,000
Aegis Power Systems Inc [Member] | Other Operating Income (Expense) [Member]
Noncontrolling Interest [Line Items]
Deconsolidation effect in statement of operations		$ 28,000
Mission Power Solutions Inc [Member]
Noncontrolling Interest [Line Items]
Minority interest percentage by non controlling interest		18.00%
Contingent consideration				$ 200,000	144,000
Increased in liability reassessment obligation				202,000
Noncontrolling interest		$ 216,000
Additional Paid-In Capital [Member]
Noncontrolling Interest [Line Items]
Reduction in cash, short-term interest receivable, and long-term investments					$ 5,000
Converpower Corporation [Member]
Noncontrolling Interest [Line Items]
Ownership percentage by parent in certain operating assets and cash	100.00%		100.00%
Minority interest percentage by non controlling interest	49.00%
Percentage of common shares exchanged	49.00%
Contingent consideration			$ 208,000	$ 478,000
Royalty payment description				Through June 30, 2021
Noncontrolling interest			$ 0
Percentage of control of business operations acquired			100.00%
Reduction in cash, short-term interest receivable, and long-term investments			$ 718,000
Deconsolidation effect in statement of operations			0
Increased in liability reassessment obligation				$ 448,000
Converpower Corporation [Member] | Additional Paid-In Capital [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest			$ (208,000)

Intangible Assets - Schedule of

Intangible Assets - Schedule of Patent Cost and Other Asset (Detail) - Patents [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Patent costs	$ 2,093	$ 2,427
Accumulated amortization	(1,386)	(1,598)
Finite-lived intangible assets, net	$ 707	$ 829

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 130,000	$ 134,000	$ 145,000
Patents [Member]
Finite-Lived Intangible Assets [Line Items]
Future amortization expense from patent assets held for 2018	112,000
Future amortization expense from patent assets held for 2019	107,000
Future amortization expense from patent assets held for 2020	102,000
Future amortization expense from patent assets held for 2021	93,000
Future amortization expense from patent assets held for 2022	$ 61,000

Product Warranties - Product Wa

Product Warranties - Product Warranty Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Guarantees [Abstract]
Balance at the beginning of the period	$ 214	$ 585	$ 204
Accruals for warranties for products sold in the period	346	358	715
Fulfillment of warranty obligations	(194)	(527)	(334)
Revisions of estimated obligations	(76)	(202)
Balance at the end of the period	$ 290	$ 214	$ 585

Stockholders' Equity - Addition

Stockholders' Equity - Additional information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 30, 2000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock repurchased as per November plan				$ 30,000,000
Stock repurchase program amount available	$ 8,541,000
Stock repurchase	0	0	0
Cash dividends paid to the Company		$ 750,000	$ 250,000
Subsidiaries [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash dividends on subsidiary common stock		$ 750,000	$ 250,000
2000 Plan, Vicor [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock reserved for issuance	21,976,340	14,377,880	14,594,805

Other Income (Expense), Net - C

Other Income (Expense), Net - Components of Other Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Income and Expenses [Abstract]
Rental income	$ 792	$ 462
Foreign currency gains (losses), net	323	(268)	$ (161)
Interest income	124	68	47
Gain (loss) on disposal of equipment	14	(4)	60
Credit gains on available-for-sale securities	11	13	12
Other	(2)	13	67
Total other income (expense), net	$ 1,262	$ 284	$ 25

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Sep. 30, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 31, 2017	Mar. 30, 2016	Dec. 28, 2015	Dec. 31, 2014
Income Tax Disclosure [Line Items]
Effective income tax rate				34.00%	34.00%	34.00%
Tax benefit recognized				$ 0	$ 0	$ 0
AMT credit carryforwards				736,000
Unremitted earnings reversed						274,000
Recognized tax benefit, voluntary disclosure agreements with several states						555,000
Gain from equity method investment						5,000,000
Provisional tax benefit due to new Tax Act				122,000
Untaxed accumulated unremitted foreign earnings				813,000
Valuation allowance, deferred tax assets				33,024,000	29,274,000
Increases in equity of realization of deferred tax assets valuation allowance							$ 3,485,000
Research and development tax credit carryforwards				20,019,000	13,967,000
Accrued interest				1,104,000	946,000	830,000				$ 1,254,000
Net interest expense				6,000	6,000	$ 21,000
Potential payment of interest				29,000	$ 25,000
Scenario, Plan [Member]
Income Tax Disclosure [Line Items]
Effective income tax rate			21.00%
Great Wall Semiconductor Corporation (GWS) [Member]
Income Tax Disclosure [Line Items]
Gain from equity method investment		$ 4,999,719		$ 4,999,719
Gain from equity method investment for income tax purpose		4,999,719
Gain (loss) on transaction for income tax purpose		$ 0
Aegis Power Systems Inc [Member]
Income Tax Disclosure [Line Items]
Sale of ownership interest						49.00%			49.00%
Converpower Corporation [Member]
Income Tax Disclosure [Line Items]
Ownership percentage by parent in certain operating assets and cash	100.00%							100.00%
Unremitted earnings reversed	$ 55,000
Sale of ownership interest								49.00%
Minimum [Member]
Income Tax Disclosure [Line Items]
Income tax examination period				3 years
Maximum [Member]
Income Tax Disclosure [Line Items]
Effective income tax rate				35.00%
Income tax examination period				7 years
Domestic Tax Authority [Member]
Income Tax Disclosure [Line Items]
Federal net operating loss carryforwards expiry, beginning year				2,033
Research and development tax credit carryforwards				$ 11,711,000
Net operating loss carryforwards				$ 18,351,000
Certain States [Member]
Income Tax Disclosure [Line Items]
Federal net operating loss carryforwards expiry, beginning year				2,018
Federal net operating loss carryforwards expiry, ending year				2,037
Research and development tax credit carryforwards				$ 11,714,000
Net operating loss carryforwards				$ 28,770,000

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Federal Statutory Rate on Loss before Income Taxes and before Gain from Sale of Equity Method Investment Rate to Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory federal tax rate	(34.00%)	(34.00%)	(34.00%)
State income taxes, net of federal income tax benefit	97.20%	1.90%	46.40%
Rate change due to tax reform	3441.10%
Tax credits	(1222.30%)	(13.60%)	29.90%
Increase (decrease) in valuation allowance	(936.10%)	46.50%	(138.40%)
Permanent items	(861.20%)	0.90%	21.20%
Refundable income taxes - AMT credit	(751.00%)
Foreign rate differential and deferred items	(91.80%)	(0.80%)	(18.20%)
Decrease in tax reserves	(5.10%)		(248.60%)
Capital gain on sale to noncontrolling interest		3.90%	237.80%
Decrease in unremitted Vicor Custom Power earnings		(0.90%)	(108.70%)
Book income attributable to noncontrolling interest		0.10%	47.00%
Other	(0.10%)	(0.20%)	(0.10%)
Effective income tax rate	(363.30%)	3.80%	(165.70%)

Income Taxes - Schedule of Dome

Income Taxes - Schedule of Domestic and Foreign Components of Income (Loss) Before Income Taxes and before the Gain from Sale of Equity Method Investment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic	$ (1,591)	$ (6,034)	$ 1,373
Foreign	1,493	4	(1,615)
Loss before income taxes	$ (98)	$ (6,030)	$ (242)

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Provision (Benefit) for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ (736)		$ 144
State	156	$ 172	(473)
Foreign	396	137	111
Current, Total	(184)	309	(218)
Deferred:
Federal		(55)	(274)
Foreign	(172)	(23)	91
Deferred Income Tax Expense (Benefit)	(172)	(78)	(183)
Provision (benefit) for income taxes	$ (356)	$ 231	$ (401)

Income Taxes - Schedule of Sign

Income Taxes - Schedule of Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Research and development tax credit carryforwards	$ 20,019	$ 13,967
Net operating loss carryforwards	4,918	4,902
Stock-based compensation	2,793	4,066
Investment tax credit carryforwards	2,181	1,576
Inventory reserves	2,059	3,143
Vacation accrual	1,255	1,928
Contingent consideration liabilities	148
Unrealized loss on investments	135	136
Deferred revenue	79	154
Warranty reserves	45	73
Bad debt reserves	36	52
Alternative minimum tax credit carryforward		340
Other	273	331
Total deferred tax assets	33,941	30,668
Less: Valuation allowance for deferred tax assets	(33,024)	(29,274)
Net deferred tax assets	917	1,394
Deferred tax liabilities:
Prepaid expenses	(470)	(654)
Patent amortization	(161)	(296)
Depreciation	(76)	(406)
Total deferred tax liabilities	(707)	(1,356)
Net deferred tax assets (liabilities)	$ 210	$ 38

Income Taxes - Schedule of Re76

Income Taxes - Schedule of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized tax benefits, Beginning Balance	$ 946	$ 830	$ 1,254
Additions based on tax positions related to the current year	138	125	120
Additions for tax positions of prior years	29
Settlements	(1)		(480)
Lapse of statute	(8)	(9)	(64)
Unrecognized tax benefits, Ending Balance	$ 1,104	$ 946	$ 830

Commitments and Contingencies -

Commitments and Contingencies - Summary of Future Minimum Rental Commitments under Non-Cancelable Operating Leases (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 1,742
2,019	1,152
2,020	872
2,021	467
2022 and thereafter	$ 1,002

Commitments and Contingencies78

Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$ 1,889,000	$ 1,866,000	$ 1,902,000

Segment Information - Significa

Segment Information - Significant Segment Financial Data (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net revenues	$ 58,771	$ 56,888	$ 57,709	$ 54,462	$ 48,085	$ 53,227	$ 52,941	$ 46,027	$ 227,830	$ 200,280	$ 220,194
Income (loss) from operations									(1,360)	(6,314)	(267)
Total assets	165,724				154,067				165,724	154,067	157,545
Depreciation and amortization									8,893	8,438	9,142
Operating Segments [Member] | BBU [Member]
Segment Reporting Information [Line Items]
Net revenues									151,789	151,428	173,064
Income (loss) from operations									5,615	11,750	21,743
Total assets	232,255				196,987				232,255	196,987	170,939
Depreciation and amortization									3,907	4,258	4,538
Operating Segments [Member] | VI Chip [Member]
Segment Reporting Information [Line Items]
Net revenues									61,330	39,947	36,688
Income (loss) from operations									(11,495)	(16,494)	(21,040)
Total assets	34,809				21,389				34,809	21,389	15,577
Depreciation and amortization									2,782	2,235	2,740
Operating Segments [Member] | Picor [Member]
Segment Reporting Information [Line Items]
Net revenues									26,297	16,684	17,304
Income (loss) from operations									5,400	(637)	(290)
Total assets	13,509				8,583				13,509	8,583	5,369
Depreciation and amortization									747	545	442
Operating Segments [Member] | Corporate [Member]
Segment Reporting Information [Line Items]
Income (loss) from operations									(880)	(933)	(680)
Total assets	59,550				73,253				59,550	73,253	81,824
Depreciation and amortization									1,457	1,400	1,422
Eliminations [Member]
Segment Reporting Information [Line Items]
Net revenues									(11,586)	(7,779)	(6,862)
Total assets	$ (174,399)				$ (146,145)				$ (174,399)	$ (146,145)	$ (116,164)

Segment Information - Additiona

Segment Information - Additional Information (Detail) - Customer	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Number of customers	1	1	1
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage of total net revenues	13.00%	16.40%	16.20%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | China [Member]
Segment Reporting Information [Line Items]
Percentage of total net revenues	35.80%	32.10%	34.20%

Segment Information - Schedule

Segment Information - Schedule of Net Revenues from Unaffiliated Customers by Country Based on the Location of the Customer (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 58,771	$ 56,888	$ 57,709	$ 54,462	$ 48,085	$ 53,227	$ 52,941	$ 46,027	$ 227,830	$ 200,280	$ 220,194
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue									83,871	80,603	88,136
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue									24,078	22,495	29,686
Asia Pacific [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue									114,365	91,848	94,845
All Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue									$ 5,516	$ 5,334	$ 7,527

Quarterly Results of Operatio82

Quarterly Results of Operations (Unaudited) - Summary of Unaudited Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Net revenues	$ 58,771	$ 56,888	$ 57,709	$ 54,462	$ 48,085	$ 53,227	$ 52,941	$ 46,027	$ 227,830	$ 200,280	$ 220,194
Gross margin	26,931	25,143	25,930	23,652	21,499	25,923	24,471	19,316	101,656	91,209	99,518
Consolidated net income (loss)	1,619	38	(445)	(954)	(2,686)	2,351	(550)	(5,376)	258	(6,261)	5,159
Net income (loss) attributable to noncontrolling interest	8	49	14	20	2	15	(6)	(25)	91	(14)	232
Net income (loss) attributable to Vicor Corporation	$ 1,611	$ (11)	$ (459)	$ (974)	$ (2,688)	$ 2,336	$ (544)	$ (5,351)	$ 167	$ (6,247)	$ 4,927
Net income (loss) per share attributable to Vicor Corporation:
Basic and diluted	$ 0.04	$ 0	$ (0.01)	$ (0.02)	$ (0.07)	$ 0.06	$ (0.01)	$ (0.14)	$ 0	$ (0.16)

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts (Detail) - Allowance for Doubtful Accounts [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 153,000	$ 171,000	$ 183,000
Charge (Recovery) to Costs and Expenses	6,000	(22,000)	18,000
Other Charges, Deductions		4,000	(30,000)
Balance at End of Period	$ 159,000	$ 153,000	$ 171,000