K2M 10-Q 2 May 18 2018 Q1 Quarterly report Financial data

DOCUMENT AND ENTITY INFORMATION

DOCUMENT AND ENTITY INFORMATION - shares	3 Months Ended
	Mar. 31, 2018	Apr. 25, 2018
Entity [Abstract]
Entity Registrant Name	K2M Group Holdings, Inc.
Entity Central Index Key	1,499,807
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		43,395,624

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 17,192	$ 23,964
Accounts receivable, net	51,257	50,474
Inventory, net	77,394	71,424
Prepaid expenses and other current assets	6,790	7,842
Total current assets	152,633	153,704
Property, plant and equipment, net	48,053	49,200
Surgical instruments, net	27,776	26,250
Goodwill	121,814	121,814
Intangible assets, net	18,768	18,899
Other assets	3,934	3,260
Total assets	372,978	373,127
Current liabilities:
Current maturities under capital lease obligation	1,161	1,122
Accounts payable	25,454	20,495
Accrued expenses	18,794	22,233
Accrued payroll liabilities	9,201	10,214
Total current liabilities	54,610	54,064
Bank line of credit	7,000	0
Convertible senior notes	39,790	39,176
Capital lease obligation, net of current maturities	33,514	33,812
Deferred income taxes, net	3,360	3,360
Other liabilities	342	316
Total liabilities	138,616	130,728
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.001 par value, 750,000,000 shares authorized; 43,404,374 and 43,389,576 shares issued and 43,388,409 and 43,373,611 shares outstanding, respectively	43	43
Additional paid-in capital	492,602	491,012
Accumulated deficit	(260,619)	(249,221)
Accumulated other comprehensive income	2,647	876
Treasury stock, at cost, 15,965 and 15,965 shares, respectively	(311)	(311)
Total stockholders’ equity	234,362	242,399
Total liabilities and stockholders’ equity	$ 372,978	$ 373,127

CONSOLIDATED BALANCE SHEETS (Un

CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, par value per share (in usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	750,000,000	750,000,000
Common stock, shares issued (in shares)	43,404,374	43,389,576
Common stock, shares outstanding (in shares)	43,388,409	43,373,611
Treasury stock, (in shares)	15,965	15,965

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenue	$ 67,876	$ 61,885
Cost of revenue	24,419	21,479
Gross profit	43,457	40,406
Operating expenses:
Research and development	5,660	5,250
Sales and marketing	32,732	30,474
General and administrative	15,082	13,754
Total operating expenses	53,474	49,478
Loss from operations	(10,017)	(9,072)
Other expense, net:
Foreign currency transaction gain (loss)	478	(27)
Interest expense	(1,782)	(1,732)
Total other expense, net	(1,304)	(1,759)
Loss before income taxes	(11,321)	(10,831)
Income tax expense	77	42
Net loss	$ (11,398)	$ (10,873)
Basic and diluted (in dollars per share)	$ (0.26)	$ (0.26)
Weighted average common shares outstanding:
Basic and diluted (in shares)	43,118,112	42,224,734

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (11,398)	$ (10,873)
Other comprehensive income:
Foreign currency translation adjustment	1,771	363
Other comprehensive income	1,771	363
Comprehensive loss	$ (9,627)	$ (10,510)

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY (Unaudited) - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning Balance (in shares) at Dec. 31, 2017	43,373,611	43,389,576				15,965
Beginning Balance at Dec. 31, 2017	$ 242,399	$ 43	$ 491,012	$ (249,221)	$ 876	$ (311)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(11,398)			(11,398)
Other comprehensive income	1,771				1,771
Stock-based compensation	$ 1,451		1,451
Issuances and exercise of stock-based compensation benefit plans, net of income tax (in shares)	14,798	14,798				0
Issuances and exercise of stock-based compensation benefit plans, net of income tax	$ 139	$ 0	139			$ 0
Ending Balance (in shares) at Mar. 31, 2018	43,388,409	43,404,374				15,965
Ending Balance at Mar. 31, 2018	$ 234,362	$ 43	$ 492,602	$ (260,619)	$ 2,647	$ (311)

CONDENSED CONSOLIDATED STATEME7

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net loss	$ (11,398)	$ (10,873)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	5,546	7,195
Provision for inventory reserves	1,305	1,146
Stock-based compensation expense	1,451	1,541
Accretion of discounts and amortization of issuance costs of convertible senior notes	632	570
Changes in operating assets and liabilities:
Accounts receivable	(320)	438
Inventory	(6,859)	(1,263)
Prepaid expenses and other assets	877	(4,032)
Accounts payable, accrued expenses, and accrued payroll liabilities	227	431
Net cash used in operating activities	(8,539)	(4,847)
Investing activities
Purchases of surgical instruments	(4,479)	(3,157)
Purchases of property, plant and equipment	(840)	(1,553)
Changes in cash restricted for leasehold improvements	0	61
Purchase of intangible assets	(17)	(23)
Net cash used in investing activities	(5,336)	(4,672)
Financing activities
Borrowings on bank line of credit	7,000	0
Payments under capital lease	(259)	(223)
Issuances and exercise of stock-based compensation benefit plans, net of income tax	139	2,744
Net cash provided by financing activities	6,880	2,521
Effect of exchange rate changes on cash and cash equivalents	223	67
Net change in cash and cash equivalents	(6,772)	(6,931)
Cash and cash equivalents at beginning of period	23,964	45,511
Cash and cash equivalents at end of period	17,192	38,580
Significant non-cash investing activities
Additions to property, plant and equipment	150	750
Reductions to property, plant and equipment from earned grant incentives	395	0
Cash paid for:
Income taxes	1	64
Interest	$ 1,087	$ 1,090

GENERAL AND SUMMARY OF SIGNIFIC

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES In this Quarterly Report on Form 10-Q, unless the context otherwise requires, references to “K2M,” “the Company,” “we,” “us” and “our,” refer to K2M Group Holdings, Inc. together with its consolidated subsidiaries. We are a global medical device provider of complex spine and minimally invasive solutions focused on achieving three-dimensional Total Body Balance. Since our inception, we have designed, developed and commercialized innovative complex spine and minimally invasive spine technologies and techniques used by spine surgeons to treat some of the most complicated spinal pathologies. K2M has leveraged these core competencies into Balance ACS™, a platform of products, services and research to help surgeons achieve three-dimensional spinal balance across the axial, coronal and sagittal planes, with the goal of supporting the full continuum of care to facilitate quality patient outcomes. The Balance ACS platform, in combination with our technologies, techniques and leadership in the 3D-printing of spinal devices, enable us to compete favorably in the global spinal surgery market. Unaudited Interim Results The accompanying condensed consolidated balance sheets as of March 31, 2018 and December 31, 2017 , the condensed consolidated statements of operations, the condensed consolidated statements of comprehensive loss for the three months ended March 31, 2018 and 2017 , the condensed consolidated statement of changes in stockholders’ equity for the three months ended March 31, 2018 , and the condensed consolidated statements of cash flows for the three months ended March 31, 2018 and 2017 are unaudited. The unaudited interim consolidated financial statements have been prepared on the same basis of accounting as the annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include normal recurring adjustments, necessary to present fairly our financial position and results of operations and cash flows for the periods presented. The results for the three months ended March 31, 2018 are not necessarily indicative of future results. All information as of March 31, 2018 and for the three month periods ending March 31, 2018 and 2017 within these notes to the condensed consolidated financial statements is unaudited. Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and all of its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Revenue Recognition We adopted ASU 2014-09, Revenue from Contracts with Customers (“Topic 606”), with a date of initial adoption of January 1, 2018. In preparing for the adoption of the new standard, we reviewed our revenue generating activities, identified the performance obligations related to those activities, and determined the appropriate timing and measurement of revenue related to the performance obligations in accordance with the standard. We applied Topic 606 retrospectively to each period reported, however, based on the results of our evaluation, there were no changes to our historical condensed consolidated financial statements for the three months ended March 31, 2017 as a result of this adoption. For revenue recognition arrangements that we determine are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies a performance obligation. We only apply the five-step model to arrangements that meet the definition of a contract under Topic 606, including when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, we will evaluate the goods or services promised within each contract related performance obligations, and assesses whether each promised good or service is distinct. We then recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. In our direct markets, we make our products available to hospitals that purchase specific products for use in a surgery on a case by case basis. We recognize revenue upon the use of such products in the completion of a surgical procedure following a receipt of a delivered order confirming that such products have been used in such procedure. In certain instances, hospital customers may purchase our products in advance of a surgical procedure. Revenue from these transactions is recognized following the completion of our performance obligations associated with the transaction which are distinct under the contract which typically includes our shipment of the purchased products and transfer of control to the hospital customer at the point of delivery. International sales outside of our direct markets are contracted with international distributors, who then resell our products their hospital customers. We recognize revenue upon completion of our performance obligations which includes shipment of the product to the distributor, who accepts title and control at the point of shipment. For these transactions, control transfers to the customer at the point of shipment. We recognize revenue at the transaction price that reflects the net consideration to which we expect to be entitled in exchange for our surgical products. If the transaction price includes variable consideration such as a discount, rebate, right of return or other sales incentives that reduce the transaction price such variable consideration is estimated when revenue is recognized based on the expected value approach. If taxes should be collected from customers relating to product sales and remitted to governmental authorities, they will be excluded from revenue. We expense incremental costs of obtaining a contract when incurred if the expected amortization period of the asset that the Company would have recognized is one year or less. We have determined that our contracts are short-term in nature and therefore no contract costs have been capitalized. Net Loss per Share Basic net loss per common share is determined by dividing the net loss allocable to common stockholders by the weighted average number of common shares outstanding during the periods presented, without consideration of common stock equivalents. Diluted loss per share is computed by dividing the net loss allocable to common stockholders by the weighted average number of shares of common stock and common stock equivalents outstanding for the period. The treasury stock method is used to determine the dilutive effect of our stock option grants. The if-converted method is used to determine the dilutive effect of the convertible senior notes due 2036 (the “Notes”). The weighted average shares used to calculate both basic and diluted loss per share are the same because common stock equivalents were excluded in the calculation of diluted loss per share because their effect would be anti-dilutive. Although included in our outstanding shares total as of March 31, 2018 and 2017 , shares of restricted stock are contingently issuable until their restrictions lapse and have been excluded from the weighted average shares outstanding. Foreign Currency Translation and Other Comprehensive Loss Our results of operations and cash flows are subject to fluctuations due to changes in foreign currency exchange rates. Our reporting currency is the U.S. dollar, which is also the functional currency of our domestic entities, while the functional currency of our foreign subsidiaries are the British Pound, Euro and Swiss Franc. Assets and liabilities denominated in foreign currencies are translated at the rate of exchange on the balance sheet date. Revenues and expenses are translated using the average exchange rate for the period. Net gains and losses resulting from the translation of foreign financial statements are recorded in other comprehensive income (loss). Net foreign currency gains or losses resulting from transactions in currencies other than the functional currencies are included in other expense, net on the consolidated statements of operations. Recently Adopted and Issued Accounting Pronouncements We adopted the following pronouncements in the first quarter of 2018: In August 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-15, Statement of Cash Flows (Topic 230), Classification of Certain Cash Receipts and Cash Payments, which eliminates the diversity in practice related to the classification of certain cash receipts and payments for debt prepayment or extinguishment costs, the maturing of a zero coupon bond, the settlement of contingent liabilities arising from a business combination, proceeds from insurance settlements, distributions from certain equity method investors and beneficial interests obtained in a financial asset securitization. It also provides clarifications related to separately identifiable cash-flows and application of the predominance principle based on evaluating the source and nature of the underlying cash flows when determining whether it is a financing, investing, operating or a combination of cash flow classifications. We adopted ASU 2016-15 effective January 1, 2018. The adoption did not have an impact on our financial position, results of operations or cash flows. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), Restricted Cash, which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. ASU 2016-18 indicates that these amounts should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. This amendment to ASU 2016-18 does not provide a definition of restricted cash or restricted cash equivalents. We adopted ASU 2016-18 effective January 1, 2018. The update did not have a material impact on our financial position, results of operations or cash flows. In January 2017, the FASB issued ASU 2017-04, Goodwill and Other (Topic 350), Simplifying the Test for Goodwill Impairment, which no longer requires an entity to measure a goodwill impairment loss by comparing the implied fair value to the carrying value of a reporting unit’s goodwill. Instead, any goodwill impairment charge will be recognized as the excess of a reporting unit’s carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit. In addition, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. This update does not affect the optional qualitative assessment of goodwill impairment. ASU 2017-04 will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. This guidance should be applied prospectively, with earlier application permitted for goodwill impairment tests with measurement dates after January 1, 2017. We adopted ASU 2017-04 effective January 1, 2018. The adoption did not have an impact on our financial position, results of operations or cash flows. In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718), Scope of modification accounting, which provides guidance about which changes to the terms of a share-based payment award should be accounted for as a modification. Under ASU 2017-09, a change to an award should be accounted for as a modification unless the fair value of the modified award is the same as the original award, inputs to the valuation technique used to value the award does not change, the vesting conditions do not change, and the classification as an equity or liability instrument do not change. This guidance should be applied prospectively to an award modified on or after date of the adoption. We adopted ASU 2017-09 effective January 1, 2018. The adoption did not have an impact on our financial position, results of operations or cash flows. Accounting Pronouncements we will adopt at a later date: In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires lessees to recognize the following for all leases (with the exception of short-term leases) at the commencement date: (i) a lease liability, which is a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis; and (ii) a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. The revised guidance must be applied on a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. Public companies will be required to comply with the guidance in 2019, and interim periods within that year. Early adoption is permitted for all entities. We are presently evaluating the impact of this guidance. In March 2018, the FASB issued ASU 2018-05, Income Taxes (Topic 740), Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 (“SAB” No. 118”), to state the income tax accounting implications of the Tax Cuts and Jobs Act (“New Tax Act”), which clarifies the measurement period time frame, changes in subsequent reporting periods and reporting requirements as a result of the New Tax Act of 2017. In accordance with SAB No. 118, a company must reflect the income tax effects of those aspects of the New Tax Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the New Tax Act is incomplete but it is able to determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the New Tax Act. SAB No. 118 provides a measurement period that should not extend beyond one year and it begins in the period that includes the enactment date which was December 22, 2017. We have not completed the accounting for the income tax effects of certain elements of the New Tax Act, which will become effective in future years. When additional guidance and regulations enable us to finalize certain tax positions, we will reflect the impact of this ASU 2018-05 on the tax provision and deferred tax calculation as of December 31, 2018.

ACCOUNTS RECEIVABLE

ACCOUNTS RECEIVABLE	3 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
ACCOUNTS RECEIVABLE	ACCOUNTS RECEIVABLE The following table summarizes accounts receivable, net of allowances: March 31, December 31, Accounts receivable $ 53,625 $ 52,820 Allowances (2,368 ) (2,346 ) Accounts receivable, net $ 51,257 $ 50,474

INVENTORY

INVENTORY	3 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY The following table summarizes inventory, net of allowances: March 31, December 31, Finished goods $ 116,999 $ 109,342 Inventory allowances (39,605 ) (37,918 ) Inventory, net $ 77,394 $ 71,424 Inventory includes surgical instruments available for sale with a carrying value of $ 8,902 and $ 8,493 at March 31, 2018 and December 31, 2017 , respectively.

PREPAID EXPENSES AND OTHER CURR

PREPAID EXPENSES AND OTHER CURRENT ASSETS	3 Months Ended
	Mar. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
PREPAIDS EXPENSES AND OTHER CURRENT ASSETS	PREPAID EXPENSES AND OTHER CURRENT ASSETS The following table summarizes prepaid expenses and other current assets: March 31, December 31, Prepaid expenses $ 3,840 $ 3,419 Other 2,950 4,423 Total $ 6,790 $ 7,842

PROPERTY, PLANT AND EQUIPMENT

PROPERTY, PLANT AND EQUIPMENT	3 Months Ended
	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT	PROPERTY, PLANT AND EQUIPMENT The following table summarizes property, plant and equipment: Estimated Useful Lives March 31, December 31, Buildings under capital lease 16 years $ 26,469 $ 26,469 Leasehold improvements, including property under capital lease 15 years 19,870 20,222 Equipment 3-5 years 4,612 4,290 Software 3 years 8,385 7,784 Computer equipment 3 years 1,198 1,165 Furniture and office equipment 5-7 years 3,828 3,823 Vehicles and other 3 years 668 878 Total 65,030 64,631 Less accumulated depreciation and amortization (16,977 ) (15,431 ) Property, plant and equipment, net $ 48,053 $ 49,200 Depreciation and amortization expense for property, plant and equipment was $ 1,525 and $ 1,361 for the three months ended March 31, 2018 and 2017 , respectively. Included in this total is amortization expense for buildings and leasehold improvements under capital lease of $ 416 for each of the three months ended March 31, 2018 and 2017 . Interest expense on the capital lease obligation was $ 564 and $ 580 for the three months ended March 31, 2018 and 2017 , respectively.

SURGICAL INSTRUMENTS

SURGICAL INSTRUMENTS	3 Months Ended
	Mar. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
SURGICAL INSTRUMENTS	SURGICAL INSTRUMENTS The following table summarizes surgical instruments: March 31, December 31, Surgical instruments $ 76,803 $ 72,018 Less accumulated depreciation and allowances (49,027 ) (45,768 ) Surgical instruments, net $ 27,776 $ 26,250 Depreciation and allowance expense for surgical instruments was $ 3,259 and $ 2,516 for the three months ended March 31, 2018 and 2017 , respectively.

INTANGIBLE ASSETS

INTANGIBLE ASSETS	3 Months Ended
	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS	INTANGIBLE ASSETS Intangible assets, net comprise the following: March 31, 2018 Estimated Useful Lives Gross Accumulated Amortization Net Indefinite-lived intangible assets: Trademarks — $ 12,900 $ — $ 12,900 In-process research and development — 900 — 900 Other — 251 — 251 Subtotal 14,051 — 14,051 Subject to amortization Developed technology 4 - 6 years 62,000 (61,825 ) 175 Licensed technology 4 - 6 years 52,800 (52,610 ) 190 Customer relationships 4 - 7 years 29,700 (29,700 ) — Patents and other 2 - 17 years 6,078 (1,726 ) 4,352 Subtotal 150,578 (145,861 ) 4,717 Intangible assets, net $ 164,629 $ (145,861 ) $ 18,768 December 31, 2017 Estimated Useful Lives Gross Accumulated Amortization Net Indefinite-lived intangible assets: Trademarks — $ 12,900 $ — $ 12,900 In-process research and development — 900 — 900 Other — 242 — 242 Subtotal 14,042 — 14,042 Subject to amortization Developed technology 4 - 6 years 62,000 (61,808 ) 192 Licensed technology 4 - 6 years 52,800 (52,602 ) 198 Customer relationships 4 - 7 years 29,700 (29,700 ) — Patents and other 2 - 17 years 6,060 (1,593 ) 4,467 Subtotal 150,560 (145,703 ) 4,857 Intangible assets, net $ 164,602 $ (145,703 ) $ 18,899 Amortization expense of intangible assets was $ 158 and $ 2,373 for the three months ended March 31, 2018 and 2017 , respectively. As of March 31, 2018 , the expected amortization expense for the remainder of 2018 and the following four years and thereafter is as follows: March 31, 2018 2018 $ 471 2019 604 2020 575 2021 516 2022 516 Thereafter 2,035 Total $ 4,717

ACCRUED EXPENSES

ACCRUED EXPENSES	3 Months Ended
	Mar. 31, 2018
Payables and Accruals [Abstract]
ACCRUED EXPENSES	ACCRUED EXPENSES Accrued expenses consist of the following: March 31, December 31, Accrued commissions $ 8,013 $ 9,495 Accrued royalties 2,830 3,489 Other 7,951 9,249 Total $ 18,794 $ 22,233

DEBT

DEBT	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
DEBT	DEBT Revolving Credit Facility We maintain a senior secured credit facilities credit agreement (as amended from time to time) with Silicon Valley Bank and Comerica Bank as Lenders, which is secured primarily by the assets of our operating subsidiaries in the United States and United Kingdom. On October 6, 2017, we entered into an amendment to the credit agreement, which extended its maturity date from April 26, 2018 to April 26, 2019, among other changes. As amended, the credit facility consists of revolving credit facility of $ 55,000 , with a sub-facility for letters of credit in the aggregate availability amount of $ 10,000 and a swingline sub-facility in the aggregate availability amount of $ 5,000 . As of March 31, 2018 , there was $ 7,000 outstanding and accrued interest at a rate of 5.50% under our revolving credit facility. The revolving credit facility contains various financial covenants and negative covenants with which we must maintain compliance, including a consolidated adjusted quick ratio for K2M, Inc., K2M UK Limited and select subsidiaries of not less than 1.20 : 1.00 as of the last day of any month, restrictive covenants which limits our ability to pay dividends on common stock and make certain investments, and the provision of certain financial reporting and company information as required. We were in compliance with all the financial and other covenants of the credit facility at March 31, 2018 . We incurred interest expense of $ 19 and $ 0 related to the credit facility and amortization expense of loan issuance fees was $ 17 and $ 60 for the three months ended March 31, 2018 and 2017 , respectively. As of March 31, 2018 , we had $ 34,591 of unused borrowing capacity under the revolving credit facility, net of an issued but undrawn letter of credit for $ 6,000 , representing a security deposit on the corporate headquarters and operations facilities lease. Convertible Senior Notes In August 2016, we issued $ 50,000 aggregate principal amount of the Notes due August 15, 2036 unless earlier converted, redeemed or repurchased by us. The Notes pay interest at an annual rate of 4.125% , payable semi-annually in arrears on February 15 and August 15 of each year. The Notes are governed by an indenture between the Company and The Bank of New York Mellon. The Notes are senior, unsecured obligations and are equal in right of payment with our existing and future senior, unsecured indebtedness, senior in right of payment to our existing and future indebtedness that is expressly subordinated to the Notes, and effectively subordinated to our existing and future secured indebtedness, to the extent of the value of the collateral securing that indebtedness. The Notes are structurally subordinated to all existing and future indebtedness and other liabilities, including trade payables, and (to the extent we are not a holder thereof) preferred equity, if any, of our subsidiaries. Interest expense related to the Notes was $ 1,130 and $ 1,065 for the three months ended March 31, 2018 and 2017 , respectively. These amounts included accretion expense of the debt discounts of $ 614 and $ 550 for the three months ended March 31, 2018 and 2017 , respectively. As of March 31, 2018 , the fair value of the Notes was $ 45,447 .

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION As of March 31, 2018 , there was a total of 1,386,071 shares of common stock available for future grants under our stock purchase and equity award or incentive plans. The following table summarizes the stock-based compensation expense by financial statement line item and type of award: Three Months Ended March 31, 2018 2017 Cost of revenue $ 27 $ 45 Research and development 36 86 Sales and marketing 239 360 General and administrative 1,149 1,050 Total $ 1,451 $ 1,541 Three Months Ended March 31, 2018 2017 Stock options $ 716 $ 811 Restricted stock 580 349 Restricted stock units (“RSUs”) 84 260 Employee Stock Purchase Plan 71 121 Total $ 1,451 $ 1,541 The following table summarizes stock option plans activity: Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value (1) Outstanding at December 31, 2017 3,165,387 $ 14.26 5.88 $ 15,567 Granted 2,913 20.72 Exercised (14,798 ) 9.34 Expired (2,058 ) 10.74 Forfeited (4,143 ) 18.12 Outstanding at March 31, 2018 3,147,301 $ 14.28 5.65 $ 17,698 Vested: At March 31, 2018 2,331,150 $ 12.35 4.62 $ 16,354 Expected to vest: At March 31, 2018 816,151 $ 19.80 1.64 $ 1,344 (1) Calculated using the fair market value per-share of our common stock as of March 31, 2018 and December 31, 2017 of $ 18.95 and $ 18.00 , respectively. A summary of restricted stock and RSU activity during the three months ended March 31, 2018 is as follows: Restricted Stock Restricted Stock Units Number of Shares Weighted-Average Grant Date Fair Value Weighted-Average Remaining Term (years) Number of Shares Weighted-Average Grant Date Fair Value Weighted-Average Remaining Term (years) Non-vested at December 31, 2017 265,684 $ 19.46 2.03 46,247 $ 15.83 2.28 Vested — — — — Granted — — 1,206 20.72 Forfeited — — — — Non-vested at March 31, 2018 265,684 $ 19.46 1.85 47,453 $ 16.56 2.06 Vested or expected to vest: At March 31, 2018 265,684 $ 19.46 1.85 47,453 $ 16.56 2.06

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Intellectual Property In the normal course of business, we enter into agreements to obtain the rights to certain intellectual property. In addition to royalty payments based on the sale of the underlying product incorporating such intellectual property, these agreements may require an up-front payment and/or milestone payments under certain conditions such as when regulatory approval is received, cumulative sales milestones or subscriber levels are achieved and other events. Typically, we have certain rights to cancel these agreements, with notice, without additional payments due other than the amount due at the time of cancellation. Royalties ranging from 2% to 10% of net sales may be due on the sale of related products under these agreements and some of the agreements contain minimum annual royalty amounts. As of March 31, 2018 , several of these agreements could require us to make additional payments should certain conditions be met in the future. Of these amounts, (i) up to $ 16,515 would be paid following the receipt of regulatory applications and approvals in the United States. (ii) up to $ 1,500 would be paid following attainment of certain subscriber levels as of July 2018, July 2019 and July 2020, and (iii) up to $ 300 would be paid based on completion of software development in 2018 related to our Balance ACS platform. In addition, milestone payments of $ 500 , $ 2,000 and $ 4,000 are due upon the achievement of net sales of related products of $ 10,000 , $ 25,000 and $ 50,000 , respectively, related to one of these agreements. A royalty payment of 7% of net sales of related products may be due until such sales reach $ 20,000 . The medical device industry is characterized by frequent claims and litigation, including claims regarding patent and other intellectual property rights as well as improper hiring practices, or other contingencies in the ordinary course of our business. We are not aware of any pending or threatened legal proceeding against us that we expect would have a material adverse effect on our business, operating results or financial condition. However, we are a party in multiple legal actions involving claimants seeking various remedies, including monetary damages, and none of the outcomes are certain or entirely within our control. We expense fees incurred for legal services as incurred.

RELATED PARTIES

RELATED PARTIES	3 Months Ended
	Mar. 31, 2018
Related Party Transactions [Abstract]
RELATED PARTIES	RELATED PARTIES In January 2017, pursuant to an underwritten public offering, our prior sponsor Welsh, Carson, Anderson & Stowe XI, L.P., and certain of its affiliates completed the sale of an additional 4,000,000 shares of our common stock. We incurred transaction fees of approximately $ 225 which are reflected as general and administrative expenses for the three months ended March 31, 2017 . We did not receive any proceeds from the sale of these shares.

INCOME TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The provision for income taxes includes both domestic and foreign minimum income taxes and changes in the valuation allowance. For the three months ended March 31, 2018 and 2017 , the income tax expense was $ 77 and $ 42 , respectively, resulting in an effective tax rate of (0.7)% and (0.4)% , respectively. The effective tax rate differs from the statutory rate due to minimum income taxes, permanent differences and changes in valuation allowances.

NET LOSS PER SHARE

NET LOSS PER SHARE	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
NET LOSS PER SHARE	NET LOSS PER SHARE The following table sets forth the computation of basic and diluted loss per share attributable to our common stockholders: Three Months Ended March 31, 2018 2017 Net loss per common share: Net loss $ (11,398 ) $ (10,873 ) Basic and diluted loss per common share: Basic and diluted weighted average common shares outstanding 43,118,112 42,224,734 Basic and diluted loss per common share $ (0.26 ) $ (0.26 ) The following outstanding securities, using the treasury stock method, were excluded from the above computations of net loss per share because their impact would be antidilutive due to the net losses during the three months ended March 31, 2018 and 2017 : Three Months Ended March 31, 2018 2017 Stock options 3,147,301 3,414,478 Restricted stock 265,684 218,505 RSUs 47,453 84,373 As discussed in Note 9, we have $ 50,000 aggregate principal amount of Notes outstanding at March 31, 2018 and 2017 . The Notes may be settled, at our election, in cash, shares of our common stock or combination of cash and shares of our common stock. For purposes of calculating the maximum dilutive impact, it is presumed that the Notes will be settled in common stock with the resulting potential common shares included in diluted earnings per share if the effect is more dilutive. The effect of the conversion of Notes is excluded from the calculation of diluted loss per share because the net loss for the three months ended March 31, 2018 and 2017 causes such securities to be antidilutive. The potential dilutive effect of these securities is shown in the table below: Three Months Ended March 31, 2018 2017 Conversion of Notes 2,799,580 2,746,680

SEGMENT AND GEOGRAPHICAL CONCEN

SEGMENT AND GEOGRAPHICAL CONCENTRATION	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
SEGMENT AND GEOGRAPHICAL CONCENTRATION	SEGMENT AND GEOGRAPHICAL CONCENTRATION Operating segments are defined as components of an enterprise for which separate discrete financial information is available and evaluated regularly by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. We manage the business globally within one reporting segment. Segment information is consistent with how management reviews the business, makes investing and resource allocation decisions and assesses operating performance. Products are sold principally in the United States. International revenue represented 26.5% of total revenue for the three months ended March 31, 2018 . Revenue earned in any individual foreign country was approximately 10% of our consolidated revenue. Our surgical sets are sold in three primary sales channels that include the Direct US, Direct international and distributor markets. One customer accounted for approximately 12.5% and 9.6% of total revenue for the three months ended March 31, 2018 and 2017 , respectively. The following table represents total revenue by geographic area, based on the location of the customer: Three Months Ended March 31, 2018 2017 United States $ 49,890 $ 46,207 International 17,986 15,678 Total $ 67,876 $ 61,885 We classify sales within the United States into three categories: complex spine pathologies, minimally invasive procedures and degenerative and other conditions. A significant portion of our international revenue is derived from our distributor partners who do not report their product usage at the surgeon or hospital level, which prevents us from providing a specific breakdown for our international revenue among the three product categories. These sales transactions are settled when we ship the product to the distributor. The following table represents domestic revenue by current procedure category: Three Months Ended March 31, 2018 2017 Complex spine $ 18,513 $ 17,136 Minimally invasive 8,375 7,872 Degenerative 23,002 21,199 49,890 46,207 International 17,986 15,678 Total $ 67,876 $ 61,885

SUBSEQUENT EVENT (Notes)

SUBSEQUENT EVENT (Notes)	3 Months Ended
	Mar. 31, 2018
Subsequent Events [Abstract]
SUBSEQUENT EVENT	SUBSEQUENT EVENT On April 27, 2018, the Company and its existing distributor in Spain and Portugal executed an exclusive agency and services agreement to replace the existing distribution agreement between the parties. Pursuant to the agreement, we acquired the distributor’s spine customer contracts and relationships and its existing K2M product inventory and instrumentation in exchange for certain outstanding receivables due from the distributor. In addition, we will become responsible for and assume risk of billing, collections and inventory management for the entity's business related to our products. We continue to evaluate our accounting for the transaction and expect to recognize revenue earned in Spain and Portugal similar to our revenue recognition policies in other direct markets.

GENERAL AND SUMMARY OF SIGNIF24

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and all of its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Revenue Recognition	Revenue Recognition We adopted ASU 2014-09, Revenue from Contracts with Customers (“Topic 606”), with a date of initial adoption of January 1, 2018. In preparing for the adoption of the new standard, we reviewed our revenue generating activities, identified the performance obligations related to those activities, and determined the appropriate timing and measurement of revenue related to the performance obligations in accordance with the standard. We applied Topic 606 retrospectively to each period reported, however, based on the results of our evaluation, there were no changes to our historical condensed consolidated financial statements for the three months ended March 31, 2017 as a result of this adoption. For revenue recognition arrangements that we determine are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies a performance obligation. We only apply the five-step model to arrangements that meet the definition of a contract under Topic 606, including when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, we will evaluate the goods or services promised within each contract related performance obligations, and assesses whether each promised good or service is distinct. We then recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. In our direct markets, we make our products available to hospitals that purchase specific products for use in a surgery on a case by case basis. We recognize revenue upon the use of such products in the completion of a surgical procedure following a receipt of a delivered order confirming that such products have been used in such procedure. In certain instances, hospital customers may purchase our products in advance of a surgical procedure. Revenue from these transactions is recognized following the completion of our performance obligations associated with the transaction which are distinct under the contract which typically includes our shipment of the purchased products and transfer of control to the hospital customer at the point of delivery. International sales outside of our direct markets are contracted with international distributors, who then resell our products their hospital customers. We recognize revenue upon completion of our performance obligations which includes shipment of the product to the distributor, who accepts title and control at the point of shipment. For these transactions, control transfers to the customer at the point of shipment. We recognize revenue at the transaction price that reflects the net consideration to which we expect to be entitled in exchange for our surgical products. If the transaction price includes variable consideration such as a discount, rebate, right of return or other sales incentives that reduce the transaction price such variable consideration is estimated when revenue is recognized based on the expected value approach. If taxes should be collected from customers relating to product sales and remitted to governmental authorities, they will be excluded from revenue. We expense incremental costs of obtaining a contract when incurred if the expected amortization period of the asset that the Company would have recognized is one year or less. We have determined that our contracts are short-term in nature and therefore no contract costs have been capitalized.
Net Loss per Share	Net Loss per Share Basic net loss per common share is determined by dividing the net loss allocable to common stockholders by the weighted average number of common shares outstanding during the periods presented, without consideration of common stock equivalents. Diluted loss per share is computed by dividing the net loss allocable to common stockholders by the weighted average number of shares of common stock and common stock equivalents outstanding for the period. The treasury stock method is used to determine the dilutive effect of our stock option grants. The if-converted method is used to determine the dilutive effect of the convertible senior notes due 2036 (the “Notes”). The weighted average shares used to calculate both basic and diluted loss per share are the same because common stock equivalents were excluded in the calculation of diluted loss per share because their effect would be anti-dilutive. Although included in our outstanding shares total as of March 31, 2018 and 2017 , shares of restricted stock are contingently issuable until their restrictions lapse and have been excluded from the weighted average shares outstanding.
Foreign Currency Translation and Other Comprehensive Loss	Foreign Currency Translation and Other Comprehensive Loss Our results of operations and cash flows are subject to fluctuations due to changes in foreign currency exchange rates. Our reporting currency is the U.S. dollar, which is also the functional currency of our domestic entities, while the functional currency of our foreign subsidiaries are the British Pound, Euro and Swiss Franc. Assets and liabilities denominated in foreign currencies are translated at the rate of exchange on the balance sheet date. Revenues and expenses are translated using the average exchange rate for the period. Net gains and losses resulting from the translation of foreign financial statements are recorded in other comprehensive income (loss). Net foreign currency gains or losses resulting from transactions in currencies other than the functional currencies are included in other expense, net on the consolidated statements of operations.
Recent Accounting Pronouncements	Recently Adopted and Issued Accounting Pronouncements We adopted the following pronouncements in the first quarter of 2018: In August 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-15, Statement of Cash Flows (Topic 230), Classification of Certain Cash Receipts and Cash Payments, which eliminates the diversity in practice related to the classification of certain cash receipts and payments for debt prepayment or extinguishment costs, the maturing of a zero coupon bond, the settlement of contingent liabilities arising from a business combination, proceeds from insurance settlements, distributions from certain equity method investors and beneficial interests obtained in a financial asset securitization. It also provides clarifications related to separately identifiable cash-flows and application of the predominance principle based on evaluating the source and nature of the underlying cash flows when determining whether it is a financing, investing, operating or a combination of cash flow classifications. We adopted ASU 2016-15 effective January 1, 2018. The adoption did not have an impact on our financial position, results of operations or cash flows. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), Restricted Cash, which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. ASU 2016-18 indicates that these amounts should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. This amendment to ASU 2016-18 does not provide a definition of restricted cash or restricted cash equivalents. We adopted ASU 2016-18 effective January 1, 2018. The update did not have a material impact on our financial position, results of operations or cash flows. In January 2017, the FASB issued ASU 2017-04, Goodwill and Other (Topic 350), Simplifying the Test for Goodwill Impairment, which no longer requires an entity to measure a goodwill impairment loss by comparing the implied fair value to the carrying value of a reporting unit’s goodwill. Instead, any goodwill impairment charge will be recognized as the excess of a reporting unit’s carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit. In addition, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. This update does not affect the optional qualitative assessment of goodwill impairment. ASU 2017-04 will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. This guidance should be applied prospectively, with earlier application permitted for goodwill impairment tests with measurement dates after January 1, 2017. We adopted ASU 2017-04 effective January 1, 2018. The adoption did not have an impact on our financial position, results of operations or cash flows. In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718), Scope of modification accounting, which provides guidance about which changes to the terms of a share-based payment award should be accounted for as a modification. Under ASU 2017-09, a change to an award should be accounted for as a modification unless the fair value of the modified award is the same as the original award, inputs to the valuation technique used to value the award does not change, the vesting conditions do not change, and the classification as an equity or liability instrument do not change. This guidance should be applied prospectively to an award modified on or after date of the adoption. We adopted ASU 2017-09 effective January 1, 2018. The adoption did not have an impact on our financial position, results of operations or cash flows. Accounting Pronouncements we will adopt at a later date: In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires lessees to recognize the following for all leases (with the exception of short-term leases) at the commencement date: (i) a lease liability, which is a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis; and (ii) a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. The revised guidance must be applied on a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. Public companies will be required to comply with the guidance in 2019, and interim periods within that year. Early adoption is permitted for all entities. We are presently evaluating the impact of this guidance. In March 2018, the FASB issued ASU 2018-05, Income Taxes (Topic 740), Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 (“SAB” No. 118”), to state the income tax accounting implications of the Tax Cuts and Jobs Act (“New Tax Act”), which clarifies the measurement period time frame, changes in subsequent reporting periods and reporting requirements as a result of the New Tax Act of 2017. In accordance with SAB No. 118, a company must reflect the income tax effects of those aspects of the New Tax Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the New Tax Act is incomplete but it is able to determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the New Tax Act. SAB No. 118 provides a measurement period that should not extend beyond one year and it begins in the period that includes the enactment date which was December 22, 2017. We have not completed the accounting for the income tax effects of certain elements of the New Tax Act, which will become effective in future years. When additional guidance and regulations enable us to finalize certain tax positions, we will reflect the impact of this ASU 2018-05 on the tax provision and deferred tax calculation as of December 31, 2018.

ACCOUNTS RECEIVABLE - (Tables)

ACCOUNTS RECEIVABLE - (Tables)	3 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Schedule of Accounts Receivable	The following table summarizes accounts receivable, net of allowances: March 31, December 31, Accounts receivable $ 53,625 $ 52,820 Allowances (2,368 ) (2,346 ) Accounts receivable, net $ 51,257 $ 50,474

INVENTORY - (Tables)

INVENTORY - (Tables)	3 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
Schedule of Current Inventory	The following table summarizes inventory, net of allowances: March 31, December 31, Finished goods $ 116,999 $ 109,342 Inventory allowances (39,605 ) (37,918 ) Inventory, net $ 77,394 $ 71,424

PREPAID EXPENSES AND OTHER CU27

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)	3 Months Ended
	Mar. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of prepaid expenses and other current assets	The following table summarizes prepaid expenses and other current assets: March 31, December 31, Prepaid expenses $ 3,840 $ 3,419 Other 2,950 4,423 Total $ 6,790 $ 7,842

PROPERTY, PLANT AND EQUIPMENT (

PROPERTY, PLANT AND EQUIPMENT (Tables)	3 Months Ended
	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following table summarizes property, plant and equipment: Estimated Useful Lives March 31, December 31, Buildings under capital lease 16 years $ 26,469 $ 26,469 Leasehold improvements, including property under capital lease 15 years 19,870 20,222 Equipment 3-5 years 4,612 4,290 Software 3 years 8,385 7,784 Computer equipment 3 years 1,198 1,165 Furniture and office equipment 5-7 years 3,828 3,823 Vehicles and other 3 years 668 878 Total 65,030 64,631 Less accumulated depreciation and amortization (16,977 ) (15,431 ) Property, plant and equipment, net $ 48,053 $ 49,200

SURGICAL INSTRUMENTS - (Tables)

SURGICAL INSTRUMENTS - (Tables)	3 Months Ended
	Mar. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Surgical Instruments	The following table summarizes surgical instruments: March 31, December 31, Surgical instruments $ 76,803 $ 72,018 Less accumulated depreciation and allowances (49,027 ) (45,768 ) Surgical instruments, net $ 27,776 $ 26,250

INTANGIBLE ASSETS - (Tables)

INTANGIBLE ASSETS - (Tables)	3 Months Ended
	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets and Goodwill	Intangible assets, net comprise the following: March 31, 2018 Estimated Useful Lives Gross Accumulated Amortization Net Indefinite-lived intangible assets: Trademarks — $ 12,900 $ — $ 12,900 In-process research and development — 900 — 900 Other — 251 — 251 Subtotal 14,051 — 14,051 Subject to amortization Developed technology 4 - 6 years 62,000 (61,825 ) 175 Licensed technology 4 - 6 years 52,800 (52,610 ) 190 Customer relationships 4 - 7 years 29,700 (29,700 ) — Patents and other 2 - 17 years 6,078 (1,726 ) 4,352 Subtotal 150,578 (145,861 ) 4,717 Intangible assets, net $ 164,629 $ (145,861 ) $ 18,768 December 31, 2017 Estimated Useful Lives Gross Accumulated Amortization Net Indefinite-lived intangible assets: Trademarks — $ 12,900 $ — $ 12,900 In-process research and development — 900 — 900 Other — 242 — 242 Subtotal 14,042 — 14,042 Subject to amortization Developed technology 4 - 6 years 62,000 (61,808 ) 192 Licensed technology 4 - 6 years 52,800 (52,602 ) 198 Customer relationships 4 - 7 years 29,700 (29,700 ) — Patents and other 2 - 17 years 6,060 (1,593 ) 4,467 Subtotal 150,560 (145,703 ) 4,857 Intangible assets, net $ 164,602 $ (145,703 ) $ 18,899
Schedule of Expected Amortization Expense	As of March 31, 2018 , the expected amortization expense for the remainder of 2018 and the following four years and thereafter is as follows: March 31, 2018 2018 $ 471 2019 604 2020 575 2021 516 2022 516 Thereafter 2,035 Total $ 4,717

ACCRUED EXPENSES - (Tables)

ACCRUED EXPENSES - (Tables)	3 Months Ended
	Mar. 31, 2018
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following: March 31, December 31, Accrued commissions $ 8,013 $ 9,495 Accrued royalties 2,830 3,489 Other 7,951 9,249 Total $ 18,794 $ 22,233

STOCK-BASED COMPENSATION - (Tab

STOCK-BASED COMPENSATION - (Tables)	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of stock-based compensation expense	The following table summarizes the stock-based compensation expense by financial statement line item and type of award: Three Months Ended March 31, 2018 2017 Cost of revenue $ 27 $ 45 Research and development 36 86 Sales and marketing 239 360 General and administrative 1,149 1,050 Total $ 1,451 $ 1,541 Three Months Ended March 31, 2018 2017 Stock options $ 716 $ 811 Restricted stock 580 349 Restricted stock units (“RSUs”) 84 260 Employee Stock Purchase Plan 71 121 Total $ 1,451 $ 1,541
Schedule of employee stock option plan activity	The following table summarizes stock option plans activity: Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value (1) Outstanding at December 31, 2017 3,165,387 $ 14.26 5.88 $ 15,567 Granted 2,913 20.72 Exercised (14,798 ) 9.34 Expired (2,058 ) 10.74 Forfeited (4,143 ) 18.12 Outstanding at March 31, 2018 3,147,301 $ 14.28 5.65 $ 17,698 Vested: At March 31, 2018 2,331,150 $ 12.35 4.62 $ 16,354 Expected to vest: At March 31, 2018 816,151 $ 19.80 1.64 $ 1,344 (1) Calculated using the fair market value per-share of our common stock as of March 31, 2018 and December 31, 2017 of $ 18.95 and $ 18.00 , respectively.
Schedule of restricted stock and RSU activity	A summary of restricted stock and RSU activity during the three months ended March 31, 2018 is as follows: Restricted Stock Restricted Stock Units Number of Shares Weighted-Average Grant Date Fair Value Weighted-Average Remaining Term (years) Number of Shares Weighted-Average Grant Date Fair Value Weighted-Average Remaining Term (years) Non-vested at December 31, 2017 265,684 $ 19.46 2.03 46,247 $ 15.83 2.28 Vested — — — — Granted — — 1,206 20.72 Forfeited — — — — Non-vested at March 31, 2018 265,684 $ 19.46 1.85 47,453 $ 16.56 2.06 Vested or expected to vest: At March 31, 2018 265,684 $ 19.46 1.85 47,453 $ 16.56 2.06

NET LOSS PER SHARE - (Tables)

NET LOSS PER SHARE - (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Earnings Per Share	The following table sets forth the computation of basic and diluted loss per share attributable to our common stockholders: Three Months Ended March 31, 2018 2017 Net loss per common share: Net loss $ (11,398 ) $ (10,873 ) Basic and diluted loss per common share: Basic and diluted weighted average common shares outstanding 43,118,112 42,224,734 Basic and diluted loss per common share $ (0.26 ) $ (0.26 )
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following outstanding securities, using the treasury stock method, were excluded from the above computations of net loss per share because their impact would be antidilutive due to the net losses during the three months ended March 31, 2018 and 2017 : Three Months Ended March 31, 2018 2017 Stock options 3,147,301 3,414,478 Restricted stock 265,684 218,505 RSUs 47,453 84,373 As discussed in Note 9, we have $ 50,000 aggregate principal amount of Notes outstanding at March 31, 2018 and 2017 . The Notes may be settled, at our election, in cash, shares of our common stock or combination of cash and shares of our common stock. For purposes of calculating the maximum dilutive impact, it is presumed that the Notes will be settled in common stock with the resulting potential common shares included in diluted earnings per share if the effect is more dilutive. The effect of the conversion of Notes is excluded from the calculation of diluted loss per share because the net loss for the three months ended March 31, 2018 and 2017 causes such securities to be antidilutive. The potential dilutive effect of these securities is shown in the table below: Three Months Ended March 31, 2018 2017 Conversion of Notes 2,799,580 2,746,680

SEGMENT AND GEOGRAPHICAL CONC34

SEGMENT AND GEOGRAPHICAL CONCENTRATION - (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Schedule of Revenue by Geographic Area	The following table represents total revenue by geographic area, based on the location of the customer: Three Months Ended March 31, 2018 2017 United States $ 49,890 $ 46,207 International 17,986 15,678 Total $ 67,876 $ 61,885
Schedule of Revenue by Products	The following table represents domestic revenue by current procedure category: Three Months Ended March 31, 2018 2017 Complex spine $ 18,513 $ 17,136 Minimally invasive 8,375 7,872 Degenerative 23,002 21,199 49,890 46,207 International 17,986 15,678 Total $ 67,876 $ 61,885

ACCOUNTS RECEIVABLE - (Details)

ACCOUNTS RECEIVABLE - (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Receivables [Abstract]
Accounts receivable	$ 53,625	$ 52,820
Allowances	(2,368)	(2,346)
Accounts receivable, net	$ 51,257	$ 50,474

INVENTORY - (Details)

INVENTORY - (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Inventory [Line Items]
Finished goods	$ 116,999	$ 109,342
Inventory allowances	(39,605)	(37,918)
Inventory, net	77,394	71,424
Surgical and Medical Instruments
Inventory [Line Items]
Inventory, net	$ 8,902	$ 8,493

PREPAID EXPENSES AND OTHER CU37

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 3,840	$ 3,419
Other	2,950	4,423
Total	$ 6,790	$ 7,842

PROPERTY, PLANT AND EQUIPMENT38

PROPERTY, PLANT AND EQUIPMENT (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total	$ 65,030	$ 64,631
Less accumulated depreciation and amortization	(16,977)	(15,431)
Property, plant and equipment, net	$ 48,053	49,200
Buildings under capital lease
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	16 years
Total	$ 26,469	26,469
Leasehold improvements, including property under capital lease
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	15 years
Total	$ 19,870	20,222
Equipment
Property, Plant and Equipment [Line Items]
Total	$ 4,612	4,290
Software
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Total	$ 8,385	7,784
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Total	$ 1,198	1,165
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Total	$ 3,828	3,823
Vehicles and other
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Total	$ 668	$ 878
Minimum | Equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Minimum | Furniture and office equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Maximum | Equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Maximum | Furniture and office equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	7 years

PROPERTY, PLANT AND EQUIPMENT -

PROPERTY, PLANT AND EQUIPMENT - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation	$ 1,525	$ 1,361
Amortization expense for capital lease	416	0
Interest expense on capital leases	$ 564	$ 580

SURGICAL INSTRUMENTS - (Details

SURGICAL INSTRUMENTS - (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Surgical instruments	$ 76,803		$ 72,018
Less accumulated depreciation and allowances	(49,027)		(45,768)
Surgical instruments, net	27,776		$ 26,250
Depreciation and allowance expense	$ 3,259	$ 2,516

INTANGIBLE ASSETS - (Details)

INTANGIBLE ASSETS - (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Intangible Asset by Major Class [Line Items]
Indefinite-lived intangible assets	$ 14,051		$ 14,042
Subject to amortization, Gross	150,578		150,560
Accumulated Amortization	(145,861)		(145,703)
Total	4,717		4,857
Intangible Assets, Gross	164,629		164,602
Intangible Assets, Net	18,768		18,899
Amortization expense	158	$ 2,373
Developed technology
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross	62,000		62,000
Accumulated Amortization	(61,825)		(61,808)
Total	175		192
Licensed technology
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross	52,800		52,800
Accumulated Amortization	(52,610)		(52,602)
Total	190		198
Customer relationships
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross	29,700		29,700
Accumulated Amortization	(29,700)		(29,700)
Total	0		0
Patents and other
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross	6,078		6,060
Accumulated Amortization	(1,726)		(1,593)
Total	4,352		4,467
Trademarks
Schedule of Intangible Asset by Major Class [Line Items]
Indefinite-lived intangible assets	12,900		12,900
In-process research and development
Schedule of Intangible Asset by Major Class [Line Items]
Indefinite-lived intangible assets	900		900
Other
Schedule of Intangible Asset by Major Class [Line Items]
Indefinite-lived intangible assets	$ 251		$ 242
Minimum | Developed technology
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	4 years		4 years
Minimum | Licensed technology
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	4 years		4 years
Minimum | Customer relationships
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	4 years		4 years
Minimum | Patents and other
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	2 years		2 years
Maximum | Developed technology
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	6 years		6 years
Maximum | Licensed technology
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	6 years		6 years
Maximum | Customer relationships
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	7 years		7 years
Maximum | Patents and other
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	17 years		17 years

INTANGIBLE ASSETS Schedule of E

INTANGIBLE ASSETS Schedule of Expected Amortization Expense (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
2,017	$ 471
2,018	604
2,019	575
2,020	516
2,021	516
Thereafter	2,035
Total	$ 4,717	$ 4,857

ACCRUED EXPENSES - (Details)

ACCRUED EXPENSES - (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued commissions	$ 8,013	$ 9,495
Accrued royalties	2,830	3,489
Other	7,951	9,249
Total	$ 18,794	$ 22,233

DEBT (Details)

DEBT (Details)	3 Months Ended
	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Aug. 11, 2016USD ($)
Debt Instrument [Line Items]
Borrowings on bank line of credit	$ 7,000,000	$ 0
Interest Expense	1,782,000	1,732,000
Letter of credit	6,000,000
Convertible Senior Notes Due 2036
Debt Instrument [Line Items]
Principal amounts of debt			$ 50,000,000
Interest rate (as a percent)			4.125%
Interest expense	1,130,000	1,065,000
Interest expense, non cash accretion of debt discount	614,000	550,000
Long-term debt	45,447,000
Revolving Credit Facility
Debt Instrument [Line Items]
Unused borrowing capacity	34,591,000
Revolving Credit Facility | October 2015 Amendment
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	55,000,000
Revolving Credit Facility | Credit Agreement 2012
Debt Instrument [Line Items]
Interest Expense	$ 19,000	0
Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Interest rate (as a percent)	5.50%
Revolving Credit Facility | Line of Credit | October 2015 Amendment
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 10,000,000
Revolving Credit Facility | Line of Credit | Credit Agreement 2012
Debt Instrument [Line Items]
Amortization of Debt Issuance Costs	17,000	$ 60,000
Revolving Credit Facility, Swing Line Loan | Line of Credit | Amended Credit Agreement 2012
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 5,000,000
Silicon Valley Bank And Comerica Bank | Revolving Credit Facility | Credit Agreement 2012
Debt Instrument [Line Items]
Line Of Credit Facility, Covenant Terms, Minimum Quick Ratio	1.20

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details)	Mar. 31, 2018shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,386,071

STOCK-BASED COMPENSATION - Allo

STOCK-BASED COMPENSATION - Allocation of Share-based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	$ 1,451	$ 1,541
Cost of revenue
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	27	45
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	36	86
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	239	360
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	1,149	1,050
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	716	811
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	580	349
Restricted stock units (“RSUs”)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	84	260
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense	$ 71	$ 121

STOCK-BASED COMPENSATION - Summ

STOCK-BASED COMPENSATION - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding Beginning Balance, Shares		3,165,387
Granted, Shares		2,913
Exercised, Shares		(14,798)
Expired, Shares		(2,058)
Forfeited, Shares		(4,143)
Outstanding Ending Balance, Shares		3,147,301	3,165,387
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning, Weighted-Average Exercise Price (in usd per share)		$ 14.26
Granted, Weighted-Average Exercise Price (in usd per share)		20.72
Exercised, Weighted-Average Exercise Price (in usd per share)		9.34
Expired, Weighted-Average Exercise Price (in usd per share)		10.74
Forfeited, Weighted-Average Exercise Price (in usd per share)		18.12
Ending, Weighted-Average Exercise Price (in usd per share)		$ 14.28	$ 14.26
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, Weighted- Average Remaining Contractual Term (years)		5 years 7 months 24 days	5 years 10 months 17 days
Outstanding, Aggregate Intrinsic Value	[1]	$ 15,567
Outstanding, Aggregate Intrinsic Value	[1]	$ 17,698	$ 15,567
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested [Abstract]
Vested, shares		2,331,150
Vested, Weighted-Average Exercise Price (in usd per share)		$ 12.35
Vested, Weighted-Average Remaining Contractual Term (years)		4 years 7 months 13 days
Vested, Aggregate Intrinsic Value		$ 16,354
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]
Vested or expected to vest, shares		816,151
Vested or expected to vest, Weighted-Average Exercise Price (in usd per share)		$ 19.80
Vested or expected to vest, Weighted-Average Remaining Contractual Term (years)		1 year 7 months 20 days
Vested or expected to vest, Aggregate Intrinsic Value	[1]	$ 1,344
Fair value valuation, estimated fair market value of stock (in dollars per share)		$ 18.95	$ 18
[1]	Calculated using the fair market value per-share of our common stock as of March 31, 2018 and December 31, 2017 of $18.95 and $18.00, respectively.

STOCK-BASED COMPENSATION - RSU

STOCK-BASED COMPENSATION - RSU and restricted stock table (Details) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding Beginning Balance, Shares	265,684
Vested (in shares)	0
Granted (in shares)	0
Forfeited (in shares)	0
Outstanding Ending Balance, Shares	265,684	265,684
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning, Weighted-Average Exercise Price (in usd per share)	$ 19.46
Vested, Weighted-Average Exercise Price (in usd per share)	0
Granted, Weighted-Average Exercise Price (in usd per share)	0
Forfeited, Weighted-Average Exercise Price (in usd per share)	0
Ending, Weighted-Average Exercise Price (in usd per share)	$ 19.46	$ 19.46
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms	1 year 10 months 6 days	2 years 10 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested or Expected to Vest, Number	265,684
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Vested and Expected to Vest, Outstanding, Weighted Average Grant Date Fair Value	$ 19.46
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	1 year 10 months 6 days
Restricted Stock and Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding Beginning Balance, Shares	46,247
Vested (in shares)	0
Granted (in shares)	1,206
Forfeited (in shares)	0
Outstanding Ending Balance, Shares	47,453	46,247
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning, Weighted-Average Exercise Price (in usd per share)	$ 15.83
Vested, Weighted-Average Exercise Price (in usd per share)	0
Granted, Weighted-Average Exercise Price (in usd per share)	20.72
Forfeited, Weighted-Average Exercise Price (in usd per share)	0
Ending, Weighted-Average Exercise Price (in usd per share)	$ 16.56	$ 15.83
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms	2 years 21 days	2 years 3 months 10 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested or Expected to Vest, Number	47,453
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Vested and Expected to Vest, Outstanding, Weighted Average Grant Date Fair Value	$ 16.56
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	2 years 21 days

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - (Details) - USD ($)	1 Months Ended	3 Months Ended
	Nov. 30, 2011	Mar. 31, 2018
Licensed technology | Minimum
Long-term Purchase Commitment [Line Items]
Future maximum royalty payments		2.00%
Licensed technology | Maximum
Long-term Purchase Commitment [Line Items]
Future maximum royalty payments		10.00%
Patents and other
Long-term Purchase Commitment [Line Items]
Milestone payment one	$ 500,000
Milestone payment two	2,000,000
Milestone payment three	4,000,000
Milestone for milestone payment one	10,000,000
Milestone for milestone payment two	25,000,000
Milestone for milestone payment three	50,000,000
Patents and other | Maximum
Long-term Purchase Commitment [Line Items]
Contingent additional payment	$ 16,515,000
In-process research and development
Long-term Purchase Commitment [Line Items]
Future maximum royalty payments	7.00%
Other Commitment, Purchase Obligation, Related Product Sales, Royalty Payment Threshold	$ 20,000,000
Proprietary Technology Purchase Agreement, Payment Due Upon Subscriber Levels
Long-term Purchase Commitment [Line Items]
Contingent additional payment		$ 1,500,000
Proprietary Technology Purchase Agreement, Payment Due Upon Completion Of Software Development
Long-term Purchase Commitment [Line Items]
Contingent additional payment		$ 0

RELATED PARTIES (Details)

RELATED PARTIES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017	Jan. 30, 2017
Related Party Transaction [Line Items]
Common stock, shares issued (in shares)		43,404,374	43,389,576
WCAS | Related Party Transaction, Sale of Stock
Related Party Transaction [Line Items]
Common stock, shares issued (in shares)				4,000,000
Underwriting commissions and transaction fees	$ 225

INCOME TAXES - (Details)

INCOME TAXES - (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Income tax (benefit) expense	$ 77	$ 42
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	(0.70%)	(0.40%)

NET LOSS PER SHARE - (Details)

NET LOSS PER SHARE - (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net loss	$ (11,398)	$ (10,873)
Basic and diluted weighted average common shares outstanding	43,118,112	42,224,734
Basic and diluted loss per common share (in dollars per share)	$ (0.26)	$ (0.26)

NET LOSS PER SHARE - Antidiluti

NET LOSS PER SHARE - Antidilutive Shares (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Aug. 11, 2016
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	3,147,301	3,414,478
Restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	265,684	218,505
Restricted stock units (“RSUs”)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	47,453	84,373
Convertible Senior Notes Due 2036
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	2,799,580	2,746,680
Convertible Senior Notes Due 2036
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Principal amounts of debt			$ 50,000,000

SEGMENT AND GEOGRAPHICAL CONC54

SEGMENT AND GEOGRAPHICAL CONCENTRATION - Narrative (Details) - Segment	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Number of reportable segments	1
Sales Revenue, Net | Geographic Concentration Risk | International
Segment Reporting Information [Line Items]
International revenue as a percentage of total revenue	26.50%
Sales Revenue, Net | Geographic Concentration Risk | United States
Segment Reporting Information [Line Items]
International revenue as a percentage of total revenue	10.00%
One Customer | Sales Revenue, Net | Customer Concentration Risk
Segment Reporting Information [Line Items]
International revenue as a percentage of total revenue	12.50%	9.60%

SEGMENT AND GEOGRAPHICAL CONC55

SEGMENT AND GEOGRAPHICAL CONCENTRATION - Revenues by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Revenue	$ 67,876	$ 61,885
Sales Revenue, Net
Segment Reporting Information [Line Items]
Revenue	67,876	61,885
United States
Segment Reporting Information [Line Items]
Revenue	49,890	46,207
United States | Sales Revenue, Net
Segment Reporting Information [Line Items]
Revenue	49,890	46,207
International | Sales Revenue, Net
Segment Reporting Information [Line Items]
Revenue	$ 17,986	$ 15,678

SEGMENT AND GEOGRAPHICAL CONC56

SEGMENT AND GEOGRAPHICAL CONCENTRATION - Revenues by Product (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue from External Customer [Line Items]
Revenue	$ 67,876	$ 61,885
United States
Revenue from External Customer [Line Items]
Revenue	49,890	46,207
United States | Complex spine
Revenue from External Customer [Line Items]
Revenue	18,513	17,136
United States | Minimally invasive
Revenue from External Customer [Line Items]
Revenue	8,375	7,872
United States | Degenerative
Revenue from External Customer [Line Items]
Revenue	23,002	21,199
International
Revenue from External Customer [Line Items]
Revenue	$ 17,986	$ 15,678