Basis of Presentation and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include the accounts of nLIGHT, Inc. and its wholly owned subsidiaries (collectively, "nLIGHT" or the "Company"). The wholly owned subsidiaries are Arbor Photonics, LLC, nLIGHT Cayman Ltd., nLIGHT Laser Technology (Shanghai) Co. Ltd, nLIGHT Oy (Finland), nLIGHT Korea Inc. and Nutronics, Inc., which the Company acquired in November 2019. All intercompany balances have been eliminated. Certain immaterial reclassifications were made to the prior period financial statements to conform to the current period presentation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, the Company evaluates its estimates, including those related to inventory valuation, allowances for doubtful accounts, warranty, sales return reserves and the recoverability of long-lived assets. Management of the Company bases its estimates on historical experience and on various other assumptions. Actual results could differ from those estimates.
Reclassifications	Reclassifications Certain immaterial reclassifications were made to the prior period financial statements to conform to the current period presentation.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with a maturity of three months or less when acquired to be cash equivalents.
Property and Equipment	Property and Equipment Property and equipment are stated at cost. Improvements and replacements are capitalized. Repair and maintenance costs are expensed as incurred. Depreciation is computed using the straight‑line method over the estimated useful life of each asset, generally 2 to 12 years.
Goodwill	Goodwill Goodwill is recorded when the purchase price of an acquisition exceeds the fair market value of the net assets acquired. Goodwill is not amortized and is tested for impairment at least annually and more frequently if material changes in events or circumstances arise. The Company performs an annual impairment review of goodwill in the fourth quarter of each year using either a qualitative assessment or a quantitative goodwill impairment test. If the qualitative assessment is selected and determines that the fair value of each reporting unit more likely than not exceeds its carrying value, no further assessment is necessary. If a quantitative test is determined necessary and an impairment is indicated, the impairment loss is recorded to the extent that the reporting unit’s carrying amount exceeds the reporting unit’s fair value. An impairment loss cannot exceed the total amount of goodwill allocated to the reporting unit.
Intangible Assets	Intangible Assets Definite-lived intangible assets consist of acquisition-related development programs and intellectual property. The intangible assets are being amortized using the straight-line method over periods of 2 to 5 years, which reflect the pattern in which economic benefits of the assets are expected to be realized.
Impairment of Long-Lived Assets	Impairment of Long‑Lived Assets Long‑lived assets, such as property and equipment, and intangibles subject to amortization, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized for the amount by which the carrying amount of the asset exceeds the fair value of the asset.
Research and Development Costs	Research and Development Costs Research and development is defined as activities aimed at developing or significantly improving a product or a process or technique whether the product or process is intended for sale or use. A process also may be used internally as a part of a manufacturing activity. Research and development costs are expensed as incurred.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability approach under which deferred income taxes are provided based upon enacted tax laws and rates applicable to the periods in which taxes become payable. The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely to be realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs.
Translation of Foreign Currencies	Translation of Foreign Currencies The Company’s international subsidiaries use their local currency as their functional currency. The financial statements of the international subsidiaries are translated to their U.S. dollar equivalents at end‑of‑period currency exchange rates for assets and liabilities and at average currency exchange rates for revenues and expenses. Translation adjustments are recorded as a component of accumulated other comprehensive loss within stockholders’ equity. Realized and unrealized foreign currency gains or losses, net are recorded in other expense within the consolidated statement of operations.
New Accounting Pronouncements	New Accounting Pronouncements ASU 2018-07 The Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting (Topic 718), in June 2018. ASU 2018-07 simplifies the accounting for share-based payments made to nonemployees so the accounting for such payments is substantially the same as those made to employees. The Company adopted ASU 2018-07 on January 1, 2019 using the modified retrospective approach with fair value measurement of unsettled liability-classified nonemployee awards, and recorded a cumulative effect adjustment of $161 thousand to beginning retained earnings. ASU 2017-04 The FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment, in January 2017. ASU 2017-04 eliminated Step 2 from the goodwill impairment test, and now requires an entity to test for goodwill impairment by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value; however, the loss recognized should not exceed the total amount of goodwill allowacted to the reporting unit. ASU 2017-04 is effective for all public business entities that are SEC filers for annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019 on a prospective basis. The Company adopted ASU 2017-04 for its annual goodwill impairment testing in the fourth quarter of 2019 with no material impact on its consolidated financial statements. ASU 2017-01 The FASB issued ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business, in January 2017. ASU 2017-01 provides a screen to determine when an integrated set of assets and activities (set) is not a business. The screen requires that when substantially all of the fair value of the gross assets acquired (or disposed of) is concentrated in a single identifiable asset or a group of similar identifiable assets, the set is not a business. The amendments in ASU 2017-01 also includes specific requirements if the screen is not met and also aligns the definition of certain elements with those of Topic 606. ASU 2017-01 was effective for for annual reporting periods of emerging growth companies beginning after December 15, 2018, including interim periods within those fiscal years, on a prospective basis. The Company adopted ASU 2017-01 in 2019 with no material impact on its consolidated financial statements. ASU 2016-13, ASU 2018-19, ASU 2019-04 and ASU 2019-05 The FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, in June 2016. ASU 2016-13 replaces the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The new standard requires that the income statement reflects the measurement of credit losses for newly recognized financial assets, as well as the changes of expected credit losses that have taken place during the period. The measurement of expected credit losses is based on relevant information related to both past and current events and circumstances. ASU 2016-13 was amended in November 2018 by ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments—Credit Losses, and again in April 2019 by ASU 2019-04, Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments, and in May 2019 by ASU 2019-05, Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief. ASU 2016-13, as amended, is effective for annual reporting periods of emerging growth companies beginning after December 15, 2020, including interim periods within those fiscal years. An entity will apply the new standard, as amended, using a modified-retrospective approach and record a cumulative effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The Company is currently evaluating the impact on its consolidated financial statements and cannot reasonably estimate the impact on its financial statements at this time. ASU 2016-02, ASU 2018-10, ASU 2018-11 and ASU 2019-01 The FASB issued ASU 2016-02, Leases (Topic 842), in February 2016. ASU 2016-02 requires the recognition of right-of-use (ROU) assets and lease liabilities on the balance sheet for virtually all leases, other than leases that meet the definition of short-term. ASU 2016-02 was amended in July 2018 by both ASU 2018-10, Codification Improvements to Topic 842, Leases, and ASU 2018-11, Leases (Topic 842): Targeted Improvements, and again in March 2019 by ASU 2019-01, Leases (Topic 842): Codification Improvements. As initially issued, the standard required lessees, upon adoption, to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach, which includes a number of optional practical expedients that entities may elect to apply. As amended, the standard allows an alternative transition method that permits entities to use its effective date as the date of initial application, and not restate comparative prior period financial information. ASU 2016-02, as amended, is effective for annual reporting periods of emerging growth companies beginning after December 15, 2019. The Company expects to implement the provisions of ASU 2016‑02, as amended, as of January 1, 2020 using the alternative modified retrospective transition method. The Company is currently evaluating the impact of this ASU, as amended, and cannot reasonably estimate the quantitative impact on the financial statements; however, the Company does expect this ASU, as amended, to have significant additional disclosure requirements. The standard provides several optional practical expedients in transition. The Company expects to elect the package of practical expedients, which permits the Company to not reassess, under the new standard, its prior conclusions about lease identification, lease classification and initial direct costs. Additionally, the Company does not expect to elect the use-of-hindsight or the practical expedient pertaining to land easements, the latter not being applicable to nLIGHT. The new standard also provides practical expedients for an entity’s ongoing accounting. Further, the Company expects to elect the short-term lease recognition exemption as well as the practical expedient to not separate lease and non-lease components for all its leases.
Accounts Receivable	Trade accounts receivable are recorded at the invoiced amount and do not bear interest. The allowance for doubtful accounts is the Company’s best estimate of the amount of probable credit losses in the Company’s existing accounts receivable. The Company determines the allowance based on historical write‑off experience and knowledge of any applicable circumstances.
Inventory	Inventory is stated at the lower of average cost and net realizable value.
Product Warranties	We offer warranties on certain products and record a liability for the estimated future costs associated with warranty claims at the time revenue is recognized. The warranty liability is based on historical experience, any specifically identified failures, and our estimate of future costs.
Revenue Recognition	Contract balances - The timing of revenue recognition may differ from the timing of invoicing to customers. Accounts receivable is recorded at the invoiced amount, net of an allowance for doubtful accounts. A receivable is recognized in the period we deliver goods or provide services or when our right to consideration is unconditional. A contract asset is recorded when we have performed under the contract but our right to consideration is conditional on something other than the passage of time. Revenue Recognition Revenue is recognized when transfer of control to the customer occurs in an amount reflecting the consideration to which the Company expects to be entitled. In order to achieve this core principle, the Company applies the following five step approach: (1) identify the contract with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations in the contract, and (5) recognize revenue when a performance obligation is satisfied. The Company considers customer purchase orders, which in some cases are governed by master sales agreements, to be the contracts with a customer. As part of its consideration of the contract, the Company evaluates certain factors including the customer's ability to pay (or credit risk). For each contract, the Company considers the promise to transfer products and/or services, each of which is distinct, as the identified performance obligations. As the Company's standard payment terms are less than one year, the Company has elected the practical expedient under ASC 606-10-32-18 to not assess whether a contract has a significant financing component. Payment terms in excess of one year are evaluated as they occur. The Company allocates the transaction price to each distinct product and/or service based on its relative standalone selling price. Master sales agreements or purchase orders from customers could include a single product or multiple products. Regardless, the contracted price with the customer is agreed to at the individual product level outlined in the customer contract or purchase order. The Company does not bundle prices; however, it does negotiate with customers on pricing for the same products based on a variety of factors (e.g., level of contractual volume). The Company has concluded that the prices negotiated with each individual customer are representative of the stand-alone selling price of the product. Revenue is recognized when control of the product and/or service is transferred to the customer (i.e., when the Company's performance obligation is satisfied), which typically occurs at shipment or delivery, depending on shipping or contract terms. The Company often receives orders with multiple delivery dates that may extend across several reporting periods. The Company allocates the transaction price of the contract to each delivery based on the product and/or service standalone selling price. The Company invoices for each scheduled delivery upon shipment or delivery and recognizes revenues for such delivery at that point, assuming transfer of control has occurred. As scheduled delivery dates are generally within one year, under the optional exemption provided by ASC 606-10-50-14a revenues allocated to future shipments of partially completed contracts are not disclosed as performance obligations for point in time revenue. Further, the Company recognizes over time revenue as per ASC 606-10-55-18 (invoice practical expedient) for its cost plus contracts and, accordingly, elects not to disclose information related to those performance obligations under ASC 606-10-50-14b. Rights of return generally are not included in customer contracts. Accordingly, product revenue is recognized upon shipment or delivery, as applicable, and transfer of control. Rights of return are evaluated as they occur. In addition, the Company has elected to account for shipping and handling as fulfillment activities and record them in cost of sales. The election of this practical expedient results in accounting treatment consistent with the Company’s historical accounting policies and therefore, this election does not impact the comparability of the financial statements. Revenue Recognition at a Point in Time - Revenues recognized at a point in time consist of sales of semiconductor lasers, fiber lasers and other related products. Revenue Recognition over Time - Revenues recognized over time generally consist of arrangements for goods and services that are structured based on the Company’s costs. Revenue for these arrangements is recognized as control transfers, which occurs as the work is performed. Billing under these arrangements generally occurs within one month after the work is completed.