K2M 10-K 18 Mar 15 2014 FY Annual report Financial data

DOCUMENT_AND_ENTITY_INFORMATIO

DOCUMENT AND ENTITY INFORMATION (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Mar. 11, 2015	Jun. 30, 2014
Entity [Abstract]
Entity Registrant Name	K2M Group Holdings, Inc.
Entity Central Index Key	1499807
Current Fiscal Year End Date	-19
Entity Filer Category	Non-accelerated Filer
Document Type	10-K
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding		39,595,130
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$171.20

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$11,411	$7,419
Accounts receivable, net	33,937	32,824
Inventory, net	52,617	39,223
Deferred income taxes	3,437	8,824
Prepaid expenses and other current assets	3,911	3,984
Total current assets	105,313	92,274
Property and equipment, net	4,220	2,978
Goodwill and intangible assets, net	163,423	186,270
Other assets, net	29,672	15,414
Total assets	302,628	296,936
Current liabilities:
Bank line of credit	0	23,500
Accounts payable	14,018	17,069
Accrued expenses	10,077	8,760
Accrued payroll liabilities	11,488	10,396
Total current liabilities	35,583	59,725
Notes to stockholders	0	19,650
Deferred income taxes	8,479	14,084
Other liabilities	112	211
Total liabilities	44,174	93,670
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.001 par value, 750,000,000 and 100,000,000 shares authorized; 37,366,098 and 22,421,509 shares issued and outstanding at December 31, 2014 and December 31, 2013, respectively	37	22
Additional paid-in capital	386,795	165,651
Accumulated other comprehensive income (loss)	1,827	-920
Accumulated deficit	-130,205	-70,568
Total stockholders’ equity	258,454	94,185
Total liabilities, redeemable convertible preferred stock, and stockholders’ equity	302,628	296,936
Series A Redeemable Convertible Preferred Stock [Member]
Current liabilities:
Redeemable convertible preferred stock	0	56,667
Series B Redeemable Convertible Preferred Stock [Member]
Current liabilities:
Redeemable convertible preferred stock	$0	$52,414

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Common stock, par value per share (in usd per share)	$0.00	$0.00
Common stock, shares authorized	750,000,000	100,000,000
Common stock, shares issued	37,366,098	22,421,509
Common stock, shares outstanding	37,366,098	22,421,509
Series A Redeemable Convertible Preferred Stock [Member]
Preferred stock, par value per share (in usd per share)	$0.00
Preferred stock, par value per share (in usd per share)		$0.00
Series B Redeemable Convertible Preferred Stock [Member]
Preferred stock, par value per share (in usd per share)	$0.00	$0.00

CONSOLIDATED_STATEMENTS_OF_OPE

CONSOLIDATED STATEMENTS OF OPERATIONS (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Revenue	$186,672	$157,584	$135,145
Cost of revenue	62,800	50,162	43,962
Gross profit	123,872	107,422	91,183
Operating expenses:
Research, development and engineering	16,302	12,402	9,031
Sales and marketing	95,323	80,183	70,163
General and administrative	60,216	59,758	57,821
Contingent consideration	0	0	-324
Total operating expenses	171,841	152,343	136,691
Loss from operations	-47,969	-44,921	-45,508
Other expense:
Foreign currency transaction (loss) gain	-4,752	1,477	1,034
Discount on prepayment of notes to stockholders	-4,825	0	0
Interest expense	-2,205	-2,810	-1,222
Total other expense, net	-11,782	-1,333	-188
Loss before income taxes	-59,751	-46,254	-45,696
Income tax benefit	-114	-8,341	-13,041
Net loss	-59,637	-37,913	-32,655
Accretion and adjustment of preferred stock to fair value	6,879
Accretion and adjustment of preferred stock to fair value		-19,439	-9,954
Net loss attributable to stockholders	($52,758)	($57,352)	($42,609)
Net loss per share attributable to common stockholders:
Basic and diluted (in dollars per share)	($1.65)	($2.58)	($1.94)
Weighted average shares outstanding:
Basic and diluted (in shares)	31,887,246	22,238,632	21,920,512

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net loss	($59,637)	($37,913)	($32,655)
Other comprehensive income (loss):
Foreign currency translation adjustment	2,747	-722	-387
Other comprehensive income (loss)	2,747	-722	-387
Comprehensive loss	($56,890)	($38,635)	($33,042)

CONSOLIDATED_STATEMENTS_OF_CHA

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY (USD $)	Total	Series A and B Convertible Preferred Stock [Member]	Series A Redeemable Convertible Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]	Security Purchases and Other [Member]	Security Purchases and Other [Member]	Security Purchases and Other [Member]	IPO [Member]	IPO [Member]	IPO [Member]
In Thousands, except Share data, unless otherwise specified	USD ($)	USD ($)	USD ($)	USD ($)	USD ($)	Series A and B Convertible Preferred Stock [Member]	USD ($)	Series A and B Convertible Preferred Stock [Member]	Series A Redeemable Convertible Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member]	USD ($)	USD ($)	USD ($)	Common Stock [Member]	Additional Paid-in Capital [Member]	USD ($)	Common Stock [Member]	Additional Paid-in Capital [Member]
						USD ($)		USD ($)	USD ($)	USD ($)					USD ($)		USD ($)	USD ($)
Beginning Balance at Dec. 31, 2011	$190,586				$22		$190,375				$189	$0
Beginning Balance (in shares) at Dec. 31, 2011					21,835,737
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	-32,655											-32,655
Other comprehensive loss	-387										-387
Stock-based compensation	2,243						2,243
Accretion of Series A and B redeemable convertible preferred stock			-7,298						-7,298
Write-up of Series B redeemable convertible preferred stock to fair value at issuance				-2,542						-2,542
Accretion of Series A and B redeemable convertible preferred stock issuance costs		-114						-114
Issuances of common stock pursuant to securities purchase and other agreements (in shares)					66,244
Issuances of common stock pursuant to securities purchase and other agreements	650						650
Exercise of options (in shares)					168,184
Exercise of options	-451						-451
Ending Balance at Dec. 31, 2012	150,032				22		182,863				-198	-32,655
Ending Balance (in shares) at Dec. 31, 2012					22,070,165
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	-37,913											-37,913
Other comprehensive loss	-722										-722
Stock-based compensation	1,588						1,588
Accretion of Series A and B redeemable convertible preferred stock			-5,304						-5,304
Write-up of Series B redeemable convertible preferred stock to fair value at issuance				-14,035						-14,035
Accretion of Series A and B redeemable convertible preferred stock issuance costs		-100						-100
Issuances of common stock pursuant to securities purchase and other agreements (in shares)					196,029
Issuances of common stock pursuant to securities purchase and other agreements	2,177						2,177
Stock option modifications	-1,910						-1,910
Exercise of options (in shares)					155,315
Exercise of options	372						372
Ending Balance at Dec. 31, 2013	94,185				22		165,651				-920	-70,568
Ending Balance (in shares) at Dec. 31, 2013	22,421,509				22,421,509
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	-59,637											-59,637
Other comprehensive loss	2,747										2,747
Stock-based compensation	5,807						5,807
Accretion of Series A and B redeemable convertible preferred stock			-1,170	-6,889
Accretion of Series A and B redeemable convertible preferred stock		-1,158						-1,158
Accretion of Series A and B redeemable convertible preferred stock issuance costs		-22						-22
Issuances of common stock pursuant to securities purchase and other agreements (in shares)														121,111			8,825,000
Issuances of common stock pursuant to securities purchase and other agreements													2,307		2,307	118,870	8	118,862
Adjustment of preferred stock to fair value prior to conversion	8,059						8,059
Common stock issued in conversion of Series A and B redeemable convertible preferred stock (in shares)						5,577,016
Common stock issued in conversion of Series A and B redeemable convertible preferred stock		83,656				6		83,650
Stock option modifications	2,077						2,077
Exercise of options (in shares)	512,933				421,462
Exercise of options	1,563				1		1,562
Ending Balance at Dec. 31, 2014	$258,454				$37		$386,795				$1,827	($130,205)
Ending Balance (in shares) at Dec. 31, 2014	37,366,098				37,366,098

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities
Net loss	($59,637)	($37,913)	($32,655)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	33,324	36,776	41,824
Provision for allowance for doubtful accounts	469	167	383
Provision for inventory reserve	583	2,285	2,908
Stock-based compensation	5,807	2,879	2,243
Amortization of issuance and discount costs included in interest expense	4,928	98	18
Decrease in contingent consideration	0	0	-324
Deferred income taxes	-218	-8,492	-13,194
Changes in operating assets and liabilities:
Accounts receivable	-2,860	-5,825	-4,303
Inventory	-13,660	-15,697	-9,543
Prepaid expenses and other assets	-8,450	-1,284	-594
Accounts payable, accrued expenses, and accrued payroll liabilities	9,552	7,916	-3,210
Net cash used in operating activities	-30,162	-19,090	-16,447
Investing activities
Purchase of surgical instruments	-12,848	-8,323	-3,604
Purchase of property and equipment	-2,905	-1,494	-1,182
Amounts placed in escrow for new corporate headquarters	-6,667	0	0
Purchase of intangible assets	-118	-117	-250
Net cash used in investing activities	-22,538	-9,934	-5,036
Financing activities
Borrowings on bank line of credit	0	3,500	9,000
Payments on bank line of credit	-23,500	-2,000	0
Payment of dividends on Series A and Series B redeemable convertible preferred stock	14,634	14,884	4,650
Proceeds from private placement of common stock	-39,212	0	0
Proceeds from issuance of Series B redeemable convertible preferred stock, net of issuance costs	0	11,574	2,395
Proceeds from issuances of common stock, net of issuance costs	121,898	0	0
Proceeds from private placement of common stock	0	2,177	650
Issuances and exercise of stock-based compensation benefit plans, net of income tax	1,563	-755	-449
Net cash provided by financing activities	56,836	29,380	16,246
Net increase (decrease) in cash and cash equivalents	-144	52	22
Cash and cash equivalents at beginning of period	3,992	408	-5,215
Cash and cash equivalents at beginning of period	7,419	7,011	12,226
Cash and cash equivalents at end of period	11,411	7,419	7,011
Significant noncash financing activities
Adjustment of preferred stock to fair value	-8,059	14,035	2,542
Cash paid for:
Income taxes	132	130	201
Interest	6,690	2,405	1,741
Series A and Series B Redeemable Convertible Preferred Stock [Member]
Financing activities
Payment of dividends on Series A and Series B redeemable convertible preferred stock	-18,547	0	0
Series A Redeemable Convertible Preferred Stock [Member]
Significant noncash financing activities
Accretion of redeemable convertible preferred stock	1,195	6,142	4,732
Series B Redeemable Convertible Preferred Stock [Member]
Significant noncash financing activities
Accretion of redeemable convertible preferred stock	($15)	($738)	$2,680

GENERAL_AND_SUMMARY_OF_SIGNIFI

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	Description of Business
	K2M Group Holdings, Inc. (the Company) was formed as a Delaware corporation on June 29, 2010. On July 2, 2010, K2M, Inc. (K2M), a company initially incorporated in 2004, entered into an Agreement and Plan of Merger (the Merger Agreement) with Altitude Group Holdings, Inc. (Altitude) and Altitude Merger Sub, Inc. (Merger Sub). Altitude was a newly formed corporation and an indirect wholly-owned subsidiary of Welsh, Carson, Anderson & Stowe XI, L.P. On August 12, 2010 (the Merger Date), upon the closing of the transactions under the Merger Agreement, Merger Sub merged with and into K2M with K2M being the surviving corporation of such merger (the Merger) and Altitude was renamed K2M Group Holdings, Inc.
	The Company is a global medical device company focused on designing, developing and commercializing innovative and proprietary complex spine technologies and techniques. The Company’s complex spine products are used by spine surgeons to treat some of the most difficult and challenging spinal pathologies, such as deformity (primarily scoliosis), trauma, and     tumor. The Company has applied its product development expertise in innovating complex spine technologies and techniques to the design, development, and commercialization of an expanding number of proprietary minimally invasive surgery, or MIS products. The Company’s MIS products are designed to allow for less invasive access to the spine and faster patient recovery times as compared to traditional open access surgical approaches for both complex spine and degenerative spine pathologies. The Company has also leveraged these core competencies in the design, development and commercialization of an increasing number of products for patients suffering from degenerative spinal conditions.
	Reverse Stock Split and Initial Public Offering
	On April 21, 2014, the Board of Directors approved a reverse stock split of the Company’s common stock such that each 2.43 shares of issued common stock were reclassified into one share of common stock. All common stock share and per-share amounts for all periods presented in these financial statements have been adjusted retroactively to reflect the reverse stock split.
	On May 13, 2014, the Company completed an initial public offering (IPO) of 8,825,000 shares of common stock at a price of $15 per share. The IPO generated net proceeds of $118,862, after deducting underwriting commissions of $9,266 and expenses of approximately $4,283. The underwriting commissions and offering costs were reflected as a reduction to the IPO proceeds received in additional paid-in capital.
	Concurrent with the closing of the IPO, the outstanding shares of the Series A redeemable convertible preferred stock (Series A Preferred) and Series B redeemable convertible preferred stock (Series B Preferred) were converted on a 2.43-to-1 basis into 5,577,016 shares of common stock. Following the closing of the IPO, there were no shares of preferred stock outstanding.
	The Company used proceeds from the IPO to pay cumulative dividends of approximately $11,932 to holders of Series A Preferred and $6,615 to holders of Series B Preferred following the conversion of the preferred stock. In addition, the Company paid approximately $23,500 to repay all outstanding indebtedness under its line of credit and $40,495 to prepay all outstanding aggregate principal and accrued interest of notes to stockholders.
	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 (US GAAP) 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 revenue and expenses during the reporting period. Actual results could differ from those estimates.
	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 the Company’s stock option grants (see Note 10) and the if-converted method is used to determine the dilutive effect of the Company’s Series A Preferred and the Series B Preferred (see Note 9). 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.
	Foreign Currency Translation and Other Comprehensive Loss
	The account balances of foreign subsidiaries are translated into U.S. dollars using exchange rates for assets and liabilities at the balance sheet date and average prevailing exchange rates for the period for revenue and expense accounts. Adjustments resulting from translation are included in other comprehensive income (loss), which is the Company’s only component of accumulated comprehensive income (loss).
	Remeasurement gains and losses from foreign currency transactions are included in other expense, net within the consolidated statements of operations in the period in which they occur.
	Cash and Cash Equivalents
	The Company considers all highly liquid investments with a maturity of three months or less when purchased to be cash equivalents.
	Restricted Cash
	The Company classifies cash as restricted when cash is unavailable for withdrawal or usage. Restrictions may include legally restricted deposits, contract bids or contracts entered into with others, or the Company’s statements of intention with regard to particular deposits.
	Accounts Receivable
	Accounts receivable are reported in the consolidated balance sheets at outstanding amounts, less the allowance for doubtful accounts. The Company performs ongoing credit evaluations of certain customers and generally extends credit without requiring collateral. The Company periodically assesses the collectability of accounts receivable considering factors such as the specific evaluation of collectability, historical collection experience and economic conditions in individual markets and records an allowance for doubtful accounts for the estimated uncollectible amount as appropriate.
	Inventory
	Inventory consists primarily of finished goods and surgical instruments available for sale and is stated at the lower of cost or market using a weighted-average cost method. The Company reviews its inventory on a periodic basis for excess, obsolete, and impaired inventory and records a reserve for the identified items.
	Property and Equipment
	Property and equipment are stated at cost net of accumulated depreciation and amortization. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts, and any resulting gain or loss is credited or charged to the consolidated statements of operations. Repairs and maintenance costs are expensed as incurred.
	Depreciation of property and equipment is computed using the straight-line method over the estimated useful lives of the respective assets. Amortization of leasehold improvements is recorded over the shorter of the life of the improvement or the remaining term of the lease using the straight-line method.
	Goodwill and Other Intangible Assets
	Goodwill represents the excess of the consideration transferred over the estimated fair value of assets acquired and liabilities assumed in connection with the Merger.
	Goodwill and indefinite lived intangible assets are not amortized but are evaluated annually or more frequently for impairment if impairment indicators exist. Such indicators include, but are not limited to (i) a significant adverse change in the business climate or environment, (ii) unanticipated competition, or (iii) adverse action or assessment by a regulator. The Company’s annual impairment date is November 1. The Company concluded it has one reporting unit. Prior to performing the annual two-step goodwill impairment test, the Company is first permitted to perform a qualitative assessment to determine if the two-step quantitative test must be completed. The qualitative assessment considers events and circumstances such as macroeconomic conditions, industry and market conditions, cost factors and overall financial performance, as well as company and specific reporting unit specifications. If after performing this assessment, the company concludes it is more likely than not that the fair value of a reporting unit is less than its carrying amount, then it is required to perform a two-step quantitative test. Otherwise, the two-step test is not required. In the first step of the quantitative test, the company is required to determine the fair value of the reporting unit and compare it to the carrying amount of the reporting unit. Fair value of the reporting unit is determined using a discounted cash flow valuation. Determining the fair value of the reporting unit is judgmental in nature and involves the use of significant estimates and assumptions. These estimates and assumptions include changes in revenue and operating margins used to project future cash flows, discount rates, and future economic and market conditions. If the carrying amount of the reporting unit exceeds the fair value of the reporting unit, the company performs the second step of the impairment test, as this is an indication that the reporting unit goodwill may be impaired. In the second step of the impairment test, the company determines the implied fair value of the reporting unit’s goodwill. If the carrying value of a reporting unit’s goodwill exceeds its implied fair value, then an impairment of goodwill has occurred and the company must recognize an impairment loss for the difference between the carrying amount and the implied fair value of goodwill.
	The Company used a qualitative assessment for its goodwill impairment testing for 2014 and 2013, and a quantitative assessment for its goodwill for such testing in 2012. The Company’s evaluation of goodwill completed during the years ended December 31, 2014, 2013 and 2012 resulted in no impairment losses.
	The Company’s indefinite-lived intangible assets include trademarks and purchased in-process research and development (IPR&D) projects, which originated from the merger and were measured at their respective estimated fair values as of the acquisition date.
	The Company used a qualitative assessment for its indefinite lived intangible asset impairment testing. The Company’s evaluation of indefinite-lived intangible assets evaluation completed during the years ended December 31, 2014, 2013 and 2012 resulted in no impairment losses.
	Finite-lived intangible assets include licensed technology, developed technology, and customer relationships and are amortized over estimated useful lives, which range from four–seven years. The Company recorded no impairment loss during the years ended December 31, 2014, 2013 and 2012.
	Other Assets
	Other long-term assets consist mainly of surgical instruments used primarily in the domestic and direct international distribution channels to implant the Company’s products. Surgical instruments are stated at cost less accumulated amortization. The Company amortizes these instruments to cost of revenues over their estimated useful life.
	The Company provides surgical instruments to its customers for use to implant its products during a surgical procedure. Following completion of the procedure, the instruments are returned to the Company upon which it will sanitize the instrument and provide it to another customer.
	As a result of the completion of an extensive evaluation of the useful life of surgical instruments in 2013, including consideration of the average age of instruments on-hand and the average age of instruments when disposed of, the Company determined that the estimated useful life of such instruments had increased to five years, from three years as previously estimated. The Company accounted for this change in the estimated useful life beginning January 1, 2013. This change had the effect of reducing cost of revenue, net loss, net loss attributable to common stockholders and net loss per share in its consolidated results of operations as follows:
		Year Ended
		December 31,
		2014		2013
	Cost of revenue	$	4,827	$	6,732
	Net loss	$	4,817	$	5,520
	Net loss attributable to common stockholders	$	4,817	$	5,520
	Net loss per share (basic and diluted)	$	0.15	$	0.25
	Impairment of Long-Lived Assets
	Long-lived assets, such as fixed assets and other finite-lived intangible assets are reviewed for impairment whenever circumstances indicate that the carrying amount of the asset may not be recoverable. The carrying amount of a long-lived asset may not be recoverable if it exceeds the sum of undiscounted cash flows expected to be generated by the asset. If an asset is determined to be impaired, the loss is measured as the amount by which the carrying amount of the asset exceeds its estimated fair value. Considerable management judgment is necessary to estimate undiscounted future cash flows. Accordingly, actual results could differ from such estimates. No events have been identified that caused an evaluation of the recoverability of the long-lived assets.
	Fair Value Measurements
	Fair value is defined in the fair value measurement accounting guidance as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date, or exit price. Assets and liabilities subject to fair value measurements are required to be disclosed within a specified fair value hierarchy. The fair value hierarchy ranks the quality and reliability of inputs or assumptions used in the determination of fair value and requires assets and liabilities carried at fair value to be classified and disclosed in one of the following categories based on the lowest level input used that is significant to a particular fair value measurement:
	•Level 1 – Defined as observable inputs such as unadjusted quoted prices in active markets for identical assets.
	•Level 2 – Defined as observable inputs other than Level 1 prices, such as quoted prices for similar assets, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.
	•Level 3 – Defined as unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions.
	The Company’s cash and cash equivalents are subject to fair value measurements. In accordance with the hierarchy, the inputs used in measuring the fair value of the cash equivalents are considered to be Level 1.
	The Company’s merger was consummated on August 12, 2010. Changes in the fair value of the contingent consideration liability resulted from either the passage of time or events occurring after the acquisition date, such as changes in the estimate of the probability of recording the Core Business Revenues. The fair value of the contingent consideration (Level 3) was measured based on the present value of the consideration expected to be  transferred using a discounted cash flow analysis. The discount rate is a significant unobservable input in such present value computations. Discount rates ranged between 15.0% and 17.5% depending on the risk associated with the cash  flows.
	The Company applies the fair value measurement accounting guidance to nonfinancial assets upon the acquisition of businesses or in conjunction with the measurement of an impairment loss of a long-lived asset, goodwill or other intangible asset under the accounting guidance for impairments.
	Financial Instruments and Concentration of Credit Risk
	The Company considers the recorded costs of certain financial assets and liabilities, including cash and cash equivalents, accounts receivable, accounts payable and accrued expenses, to approximate their fair value because of relatively short maturities at December 31, 2014 and December 31, 2013. The fair values of the bank line of credit and other long-term liabilities approximated their carrying amounts as of December 31, 2014 and December 31, 2013, based on rates and terms available to the Company at that time.
	Financial instruments that potentially subject the Company to a concentration of credit risk consist principally of cash and cash equivalents and accounts receivable. The Company maintains its cash balances with creditworthy financial institutions in the United States, and the balances may exceed, at times, the amount insured by the Federal Deposit Insurance Corporation. No single customer represented more than 10% of revenue for any period presented.
	Revenue Recognition
	Revenue is recognized when all of the following criteria are met: persuasive evidence of an arrangement exists, delivery has occurred or service has been rendered, the price to the buyer is fixed or determinable, and collectability is reasonably assured.
	The Company’s revenue in its direct markets is generated by making its products available to hospitals that purchase specific products for use in surgery on a case-by-case basis. Revenue from sales generated by use of products is recognized upon receipt of a delivered order confirming that the Company’s products have been used in a surgical procedure.
	International sales outside of its direct markets are transacted with independent distributors, who then resell the products to their hospital customers. The Company recognizes revenue upon shipment of its products to the international distributors, who accept title at point of shipment.
Shipping and Handling Costs
Shipping and handling costs are charged to sales and marketing expense in the consolidated statements of operations and amounted to $3,403, $2,311 and $2,143 for the years ended December 31, 2014, 2013 and 2012, respectively.
Research, Development, and Engineering
The Company expenses its research, development and engineering costs as incurred.
Stock-Based Compensation
The Company awards stock-based compensation primarily in the form of stock options and restricted stock units (RSUs). For stock options awarded, stock-based compensation is based on the fair value of such awards granted to employees using the Black-Scholes-Merton option pricing model and is expensed on a straight-line basis over the award's vesting period, less awards expected to be forfeited using estimated forfeiture rates.
For RSUs awarded after the Company's IPO, the stock-based compensation is based on the closing market share price of the Company's common stock on the date of award and is expensed on a straight-line basis over the award's vesting period.
The Company also recognizes stock-based compensation for participation in its 2014 Employee Stock Purchase Plan ("ESPP"). The ESPP provides for a look-back option feature that gives an option to the participant to purchase the Company's common stock at a discount to the market price for such stock. The ESPP is compensatory to the Company. The compensation costs are recognized over the offering period based on the fair value of the option granted to participants and the number of shares expected to be purchased at the end of the offering period.
Income Taxes
The Company accounts for income taxes using the liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities, their respective tax bases and operating loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the year in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in operations in the period that includes the enactment date.
Valuation allowances are established when necessary to reduce net deferred tax assets to the amount expected to be realized. Income tax expense (benefit) is the tax payable (receivable) for the period and the change during the period in deferred tax assets and liabilities.
As prescribed by the accounting guidance, the Company uses a more-likely-than-not recognition threshold based on the technical merits of the tax position taken. Tax positions that meet the more-likely-than-not recognition threshold are measured at the largest amount of the tax benefits, as determined on a cumulative probability basis, that are more-likely-than-not to be realized upon ultimate settlement in the financial statements. The Company recognizes interest and penalties related to income tax matters in income tax expense (benefit).
Redeemable Convertible Preferred Stock
The Company used the effective interest method to accrete the differences between the carrying value and the estimated redemption value of its preferred stock, such that the carrying value approximated the redemption value on the earliest possible redemption date.

ACCOUNTS_RECEIVABLE

ACCOUNTS RECEIVABLE	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
ACCOUNTS RECEIVABLE	ACCOUNTS RECEIVABLE
	Receivables consist of the following:
		December 31,
		2014			2013
	Accounts receivable	$	36,431		$	35,271
	Allowances	(2,494		)	(2,447		)
	Accounts receivable, net	$	33,937		$	32,824
	The following reflects a rollforward of the accounts receivable allowances for the years ended December 31, 2014, 2013 and 2012:
		December 31,
		2014			2013			2012
	Beginning	$	(2,447	)	$	(2,217	)	$	(2,020	)
	Additions	(436		)	(230		)	(383		)
	Write-offs	389			—			186
	Ending	$	(2,494	)	$	(2,447	)	$	(2,217	)

INVENTORY

INVENTORY	12 Months Ended
	Dec. 31, 2014
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY
	The following table summarizes the Company's inventory, net of allowances:
		December 31,
		2014			2013
	Finished goods	$	78,331		$	64,539
	Inventory allowances	(25,714		)	(25,316		)
	Inventory, net	$	52,617		$	39,223
	Inventory includes surgical instruments available for sale with a carrying value of $8,491 and $5,285 at December 31, 2014 and December 31, 2013, respectively.

PROPERTY_AND_EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERTY AND EQUIPMENT
	Property and equipment consist of the following:
		Estimated	December 31,
		Useful Lives	2014		2013
	Equipment	3 years	2,725		2,412
	Software	3 years	3,923		2,376
	Computer equipment	3 years	1,445		1,265
	Leasehold improvements	Various	1,109		1,098
	Furniture and office equipment	5 years	1,048		673
	Vehicles and other	Various	458		12
	Total		10,708		7,836
	Less accumulated depreciation and amortization		(6,488	)	(4,858	)
	Property and equipment, net		4,220		2,978
	Depreciation expense was $1,626, $1,505 and $1,589 for the years ended December 31, 2014, 2013 and 2012, respectively.

GOODWILL_AND_INTANGIBLE_ASSETS

GOODWILL AND INTANGIBLE ASSETS	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND INTANGIBLE ASSETS	GOODWILL AND INTANGIBLE ASSETS
	Goodwill and intangible assets comprise of the following:
			As of December 31, 2014
			Estimated		Gross		Accumulated			Net
			Useful Lives				Amortization
	Goodwill		—		$	121,814	$	—		$	121,814
	Indefinite-lived intangible assets:
	Trademarks				12,900		—			12,900
	In-process research and development (1)		—		900		—			900
	Other		—		278		—			278
	Subtotal				14,078		—			14,078
	Subject to amortization
	Developed technology (1)		4 - 6 years		62,000		(46,460		)	15,540
	Licensed technology		4 - 6 years		52,600		(52,175		)	425
	Customer relationships		4 - 7 years		29,700		(18,563		)	11,137
	Patents and other		2 - 17 years		1,414		(985		)	429
	Subtotal				145,714		(118,183		)	27,531
	Total				$	281,606	$	(118,183	)	$	163,423
			As of December 31, 2013
			Estimated		Gross		Accumulated			Net
			Useful Lives				Amortization
	Goodwill		—		$	121,814	$	—		$	121,814
	Indefinite-lived intangible assets:
	Trademarks		—		12,900		—			12,900
	In-process research and development (1)		—		1,500		—			1,500
	Other		—		296		—			296
	Subtotal				14,696		—			14,696
	Subject to amortization
	Developed technology (1)		4 - 6 years		61,600		(36,466		)	25,134
	Licensed technology		4 - 6 years		52,600		(43,947		)	8,653
	Customer relationships		4 - 7 years		29,700		(14,320		)	15,380
	Patents and other		2 - 17 years		1,313		(720		)	593
	Subtotal				145,213		(95,453		)	49,760
	Total				$	281,723	$	(95,453	)	$	186,270
	-1	In 2014 and 2013, a total of $400 and $0 of IPRD, respectively, was reclassified to developed technology, as the underlying products were introduced to market during the year. The assets will be amortized over a six-year period. In 2014, the Company has written-off a total of $200 for an IPR&D project that will no longer be pursued.
	Amortization expense was $22,946, $30,195 and $30,062 for the years ended December 31, 2014, 2013 and 2012, respectively.
	As of December 31, 2014, the expected amortization expense for each of the next five years and thereafter is as follows:
	2015		$	10,275
	2016		10,205
	2017		6,590
	2018		95
	2019 and thereafter		366
	Total		$	27,531

OTHER_ASSETS

OTHER ASSETS	12 Months Ended
	Dec. 31, 2014
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
OTHER ASSETS	OTHER ASSETS
	Other assets comprises the following:
		December 31,
		2014		2013
	Surgical instruments, net	$	21,392	$	15,271
	Restricted cash	8,114		—
	Other	166		143
	Total	$	29,672	$	15,414
	Surgical instruments are stated net of accumulated amortization of $18,610 and $15,007 at December 31, 2014 and December 31, 2013, respectively. Amortization expense was $6,494, $2,814 and $5,940 for the years ended December 31, 2014, 2013 and 2012, respectively.
	As of December 31, 2014, restricted cash includes amounts placed in escrow for tenant improvement costs of $6,667 for the Company's new corporate headquarters and deposits made on pending bids or contracts with customers of $1,447.

ACCRUED_EXPENSES

ACCRUED EXPENSES	12 Months Ended
	Dec. 31, 2014
Payables and Accruals [Abstract]
ACCRUED EXPENSES	ACCRUED EXPENSES
	Accrued expenses consist of the following:
		December 31,
		2014		2013
	Accrued commissions	$	4,942	$	2,837
	Accrued royalties	2,464		2,230
	Stock option awards liability	—		2,076
	Other	2,671		1,617
	Total	$	10,077	$	8,760

DEBT

DEBT	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
DEBT	DEBT
	Debt consists of the following:
		December 31,
		2014		2013
	Bank line of credit	$	—	$	23,500
	Notes to stockholders	—		22,270
	Total debt	—		45,770
	Less unamortized discounts	—		(2,620		)
	Debt, net of discounts	$	—	$	43,150
	Bank Line of Credit
	On May 13, 2014, the Company repaid all $23,500 outstanding under the bank line of credit and accrued interest of $38 using proceeds of the IPO.
	On October 21, 2014 the Company amended its revolving credit facility with Silicon Valley Bank and Comercia Bank, or the Lenders. The amended credit facility consists of a revolving credit facility of $40,000 with a sub-facility for letters of credit in the aggregate availability amount of $10,000 and a swing-line sub facility in the aggregate availability amount of $5,000. The credit facility is secured by a first priority lien on all the Company's personal property assets, including intellectual property, and matures in October 2015.
	On January 9, 2015, the Company entered into another amendment to the revolving credit facility. The amendment, among other things, amended and restated the definition of “Available Revolving Commitment” under the credit agreement in order to
	exclude the Company’s issued and outstanding letters of credit under the credit agreement’s $10,000 letter of credit
	sub-facility from the calculation of the Company’s borrowing capacity under the credit agreement. The letters of credit
	will continue to be considered when determining the Total Revolving Commitments, as defined under the credit
	agreement, which remain unchanged at $40,000.
	ABR loans under the revolving credit facility bear interest at a rate per annum equal to ABR, plus 0.75%.  LIBOR loans under the revolving credit facility bear interest at a rate per annum equal to the greater of (i) LIBOR, plus 2.50% or (ii) 3.75%. The total obligations under the amended credit facility cannot exceed (i) the lesser of the total revolving commitment of $40,000 or (ii) the borrowing base, which is calculated as (x) 85% of accounts receivable so long as certain of those accounts receivable do not exceed, in the aggregate, 50% of the borrowing base plus (y) 35% of the value of the eligible inventory provided that the contribution of the value of the eligible inventory not exceed the lesser of 40% of the borrowing base or (z) $10,000.
	For the years ended December 31, 2014, 2013 and 2012, the Company recorded interest expense of $373, $1,383 and $964, respectively, under the credit agreement and amounts of $338, $383 and $147, respectively, related to the amortization of the loan issuance fees. As of December 31, 2014, unrestricted cash plus $26,535 of unused borrowing availability under the bank line of credit was in excess of the $5,000 threshold that requires lockbox receipts to be applied against outstanding borrowings.
	The revolving credit facility, as amended contains various financial covenants and negative covenants with which the Company must maintain compliance, including a consolidated adjusted quick ratio for K2M, Inc., K2M UK Limited and select subsidiaries not less than 1.20:1.00 as of the last day of any month, as well as the provision of certain financial reporting and company information as required. In addition, there are restrictive covenants that limit the Company's ability to pay dividends on common stock and make certain investments. As of December 31, 2014, the Company was in compliance with all the covenants under the credit agreement.
	The Company had no outstanding borrowings on the revolving credit facility at December 31, 2014. As of December 31, 2014, as adjusted to give effect to the amendments entered into on October 21, 2014 and January 9, 2015, respectively, the Company had approximately $32,628 of unused borrowing availability under the revolving credit facility. As of December 31, 2014, the Company had approximately $6,100 related to two issued but undrawn letters of credit, with one letter of credit representing a $6,000 security deposit on the new corporate headquarters lease.
	Notes to Stockholders
	In January 2014, the Company issued 121,111 shares of its common stock to certain stockholders at $19.05 per share for proceeds of $2,308. In addition, K2M Holdings, Inc. issued these stockholders notes with an aggregate principal amount of $16,942 and bearing interest at 10% for cash consideration of $14,634.
	In May and June 2013, the Company issued 126,235 shares of its common stock to certain stockholders at $10.74 per share for proceeds of $1,356 and in November 2013 issued an additional 57,448 shares to certain existing shareholders at $12.73 per share for proceeds of $731. In addition, K2M Holdings, Inc. issued these stockholders notes with an aggregate principal amount of $16,970 and bearing interest at 10% for cash consideration of $14,884.
	In June 2012, the Company issued 66,244 shares of its common stock to two existing stockholders at $9.82 per share for proceeds of $650. In addition, K2M Holdings, Inc. issued these stockholders notes with an aggregate principal amount of $5,300 and bearing interest at 10% for cash consideration of $4,650.
	Following issuance of these notes, total aggregate principal amount outstanding of all notes payable to stockholders was $39,212.
	On May 13, 2014, the Company pre-paid all $39,212 principal outstanding under the notes to stockholders and accrued interest of $1,283 using proceeds of the IPO. In connection with the prepayment, the Company expensed $4,825 representing the acceleration of the issuance discounts on the notes to stockholders. Interest expense for the years ended December 31, 2014, 2013 and 2012, was $1,324, $1,410 and $275, respectively, and included amortization expense of $4,928, $98 and $18, respectively.

PREFERRED_STOCK

PREFERRED STOCK	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
PREFERRED STOCK	PREFERRED STOCK
	Redeemable Convertible Preferred Stock
	In 2010, the Company issued 6,561,680 shares of Series A Preferred for aggregate gross proceeds of $25,000 and 689,205 shares were issued to two stockholders of the Company upon reinvestment of cash received as part of the Merger.
	In 2011, the Company issued 2,624,672 shares of Series B Preferred to Company stockholders for proceeds of $10,000. In 2012, the Company issued 638,696 shares of Series B Preferred to Company stockholders for proceeds of $2,433. In 2013, the Company issued 3,037,922 shares of Series B Preferred to existing stockholders for aggregate gross proceeds of $11,574.
	On May 13, 2014, pursuant to their terms, the Company converted all outstanding Series A Preferred and Series B Preferred into 2,983,902 and 2,593,114 shares, respectively, of its common stock based on a 2.43-to-1 conversion ratio as a result of the closing of the IPO.
	The following is a rollforward of activity in the Series A Preferred and Series B Preferred accounts during the years ended December 31, 2012, 2013 and 2014, respectively.
		Series A Preferred							Series B Preferred
		Shares							Shares
		Authorized		Outstanding		Amount			Authorized		Outstanding		Amount
	Balance at December 31, 2011	7,300,000		7,250,885		$	45,793		5,249,000		2,624,672		$	19,926
	Issuance of preferred stock	—		—		—			—		638,696		2,433
	Issuance costs of preferred stock	—		—		—			—		—		(38		)
	Accretion of preferred stock to fair value	—		—		4,732			—		—		5,222
	Balance at December 31, 2012	7,300,000		7,250,885		50,525			5,249,000		3,263,368		27,543
	Issuance of preferred stock	—		—		—			1,251,000		3,037,922		11,574
	Accretion of preferred stock to fair value	—		—		6,142			—		—		13,297
	Balance at December 31, 2013	7,300,000		7,250,885		56,667			6,500,000		6,301,290		52,414
	Payment of dividend	—				(11,932		)					(6,615		)
	Accretion of preferred stock to fair value	—		—		1,195			—		—		(15		)
	Adjustment of preferred stock to fair value prior to conversion	—		—		(1,170		)	—		—		(6,889		)
	Conversion to common stock	(7,300,000	)	(7,250,885	)	(44,760		)	(6,500,000	)	(6,301,290	)	(38,895		)
	Balance at December 31, 2014	—		—		$	—		—		—		$	—
	Dividends. The holders of Series A Preferred and Series B Preferred were entitled to receive cumulative dividends at the annual rate of 10% of the Series A Accrued Value and 14% of the Series B Accrued Value (the original issue price plus accrued compounded dividends), respectively, in preference to any payment of dividends to holders of common stock. Dividends shall be payable when and if declared by the Board of Directors. To the extent that dividends were paid to holders of the common stock, holders of Series A Preferred or Series B Preferred would participate on an “if-converted” basis. On May 13, 2014, cumulative unpaid dividends of $18,547 were paid in cash to holders of the preferred stock. As of December 31, 2013, cumulative unpaid dividends of the Series A Preferred and Series B Preferred were $10,564 and $5,136, respectively.
	Redemption of Series A Preferred and Series B Preferred. At any time on or after August 12, 2017, the holders of the Series A Preferred and Series B Preferred had the right to require the Company to redeem all or a portion of their outstanding shares of preferred stock.
	The per share redemption price for each series should equal to the greater of (1) its Accrued Value or (2) the fair market value. In the absence of a readily determinable market value, the fair market value is determined by the Company’s Board of Directors, taking into consideration the enterprise value of the Company and the rights and preferences of preferred stock without giving effect to any discount based on the illiquidity of each series of preferred stock. The Company estimates the fair market value of its Series A Preferred and Series B Preferred at each reporting period, determines the greater of (1) the fair market value and (2) Series A and B Accrued Value, and accordingly, records accretion based on the difference between the carrying value and the estimated redemption amount using the effective interest method.
	Preferred Stock
	As of December 31, 2014, the Company had 100,000,000 shares of preferred stock authorized of which no shares were issued or outstanding.

STOCKBASED_COMPENSATION

STOCK-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION
	As of December 31, 2014, the Company has four stock-based compensation plans: The 2014 Employee Omnibus Incentive Plan (the "Omnibus Incentive Plan"), the ESPP, the 2010 Equity Award Plan and the 2010 Independent Agent Plan, collectively, “the Plans”. The purpose of the Plans is to provide incentives to employees, directors, agents and advisors of the Company. The Plans are administered by the Company’s board of directors or its delegates. The number, type of equity incentive, exercise or share purchase price and vesting terms are determined in accordance with the Plans, as applicable.
	The Omnibus Incentive Plan
	The Omnibus Incentive Plan was adopted to provide a means through which to attract and retain key personnel and to provide a means whereby the Company’s directors, officers, employees, consultants and advisors can acquire and maintain an equity interest in the Company. The Omnibus Incentive Plan is administered by the Compensation Committee of the Company’s board of directors. Incentive awards under the plan may take the form of incentive or non-qualified stock options, stock appreciation rights, restricted shares and restricted stock units ("RSUs") and other stock-based awards, subject to certain limitations. The committee may also designate any award as a “performance compensation award” intended to qualify as “performance-based compensation” under Section 162(m) of the Internal Revenue Code. As of December 31, 2014, there were 753,601 shares available for issuance under this plan.
	The ESPP
	The ESPP was established to provide employees and participating affiliates with an opportunity to purchase the Company’s common stock. The ESPP is intended to qualify as an “employee stock purchase plan” under Section 423 of the Internal Revenue Code. As of December 31, 2014, 384,339 shares were available for issuance under the ESPP.
	Generally, all domestic employees are eligible to participate in the ESPP if they are employed by the Company or any participating affiliate, for at least 20 hours per week. Participants will be permitted to purchase shares of the Company’s common stock through payroll deductions of no less than 1% and no more than 10% of their eligible compensation. However, during the first offering period, which commenced on May 8, 2014 and ended on December 31, 2014, participants were limited to contributions of 2% of eligible compensation. Subsequent offerings will start after the end date of the first offering period on a schedule established by the committee appointed by the Company's board of directors to administer the ESPP. Amounts deducted and accumulated by the participant will be used to purchase shares of the Company’s common stock at the end of each offering period. The purchase price of the shares will be equal to 85% of the lower of the fair value of the Company’s common stock on the first day of the offering period, or on the common stock purchase date at the end of each offering period. Participants may end their participation at any time during an offering period and will be paid their accrued contributions that have not yet been used to purchase shares of common stock. In addition, participation ends automatically upon termination of employment with the Company.
	The Company recognized approximately $80 of stock-based compensation expense on the ESPP for the year ended December 31, 2014. The Company issued 27,184 shares of common stock to ESPP participants for proceeds of $346 on December 31, 2014.
	2010 Equity Award Plan
	The Company’s 2010 Equity Award Plan (the "2010 Plan") was adopted and approved in connection with the Merger.
	Pursuant to the 2010 Plan, the Company may issue various equity awards including incentive stock options, non-qualified stock options, restricted or unrestricted stock awards, or other equity awards. Stock options awarded under the 2010 Plan will be granted with an exercise price equal to the estimated market price of the Company’s common stock on the date of grant. The options generally vest in equal installments over a four-year period based on continued service in the Company and have a ten-year contractual term. As of December 31, 2014, there were 50,546 shares of common stock available for issuance under the 2010 Equity Award Plan.
	The Company recognized the following stock-based compensation expense related to stock options issued to employees and non-employees and RSUs issued to employees which is inclusive of the amounts detailed below:
			Year Ended
			December 31,
			2014 (1)			2013 (1)				2012 (1)
	Cost of revenue		$	424		$	532			$	32
	Research, development, and engineering		439			92				136
	Sales and marketing		2,146			889				696
	General and administrative		2,798			1,366				1,379
			$	5,807		$	2,879			$	2,243
	Employees		$	5,537		$	2,664			$	2,195
	Non-employees		270			215				48
	Total		$	5,807		$	2,879			$	2,243
	-1	Stock-based compensation expense included $0, $1,291 and $0 related to stock option liability awards for the year ended December 31, 2014, 2013 and 2012, respectively.
	A summary of stock option plans activity during the year ended December 31, 2014 is as follows:
			Shares		Weighted-				Weighted-		Aggregate
					Average				Average		Intrinsic
					Exercise				Remaining		Value (1)
					Price				Contractual
									Term
									(years)
	Outstanding at December 31, 2013		4,179,119		$	8.18			5.64		$	31,434
	Granted		707,796		15.04
	Exercised		(512,933	)	6.1
	Expired		(31,888	)	4.41
	Forfeited		(64,865	)	10.9
	Outstanding at December 31, 2014(2)		4,277,229		$	9.55			5.83		$	48,418
	Vested or expected to vest:
	At December 31, 2014(3)		4,102,613		$	9.51			5.78		$	46,595
	Vested:
	At December 31, 2014		2,302,735		$	7.93			4.44		$	29,797
	-1	Calculated using the estimated fair market value per share of the Company’s common stock as on December 31, 2014 and actual per share fair market value at December 31, 2013, which was $20.87 and $15.70, respectively.
	-2	The total includes 888,174 and 963,221 performance-based options at December 31, 2014 and December 31, 2013, respectively.
	-3	Outstanding options, net of forfeiture rate.
	The total fair value of employee stock options that vested was approximately $1,386, $2,034 and $2,376 during the years ended December 31, 2014, 2013 and 2012, respectively.
	The weighted-average fair value per share of options granted by the Company was $5.54, $4.53 and $4.95 during the years ended December 31, 2014, 2013 and 2012, respectively. The fair value was determined by applying the Black-Scholes-Merton option pricing model, utilizing the following weighted-average assumptions:
			Year Ended
			December 31,
			2014		2013			2012
	Expected dividend yield		—	%	—	%		—	%
	Expected volatility		35.19-37.47%		35.42-40.00%			32.85-34.38
	Risk-free interest rate		1.79-2.18%		1.25-2.00%			0.92-1.04%
	Expected average life of options		6-7 years		7 years			6-7 years
	A discussion of management’s methodology for developing each of the assumptions used in the valuation model follows:
	•	Dividend Yield – The Company has never declared or paid dividends and has no plans to do so in the foreseeable future.
	•	Risk-Free Interest Rate – This is the U.S. Treasury rate for the week of each option grant during the year that has a term that most closely resembles the expected life of the option.
	•	Expected Life of the Option Term – This is the period of time that the options granted are expected to remain unexercised. For options granted during the years ended December 31, 2014, 2013 and 2012, the Company derived the expected life of the option based on the average midpoint between vesting and the contractual term, as the Company has little exercise history.
	•	Expected Volatility – Volatility is a measure of the amount by which a financial variable such as a share price has fluctuated (historical volatility) or is expected to fluctuate (expected volatility) during a period. The Company uses an estimated volatility based on the volatility of a number of similarly situated public companies, along with other factors deemed relevant by management.
	As of December 31, 2014 and December 31, 2013, there was approximately $4,253 and $2,318, respectively of total unrecognized compensation expense (exclusive of compensation expense related to the performance-based vesting awards), less estimated forfeitures, related to nonvested employee stock options under the Company’s stock compensation plans. As of December 31, 2014 and 2013, this expense is expected to be recognized over a weighted-average period of 2.08 and 2.54 years, respectively. The expected forfeiture rate is the estimated percentage of options granted that is expected to be forfeited or canceled on an annual basis before becoming fully vested. The Company estimates the forfeiture rate based on past turnover data, with further consideration given to the class of employees to whom the options were granted. The forfeiture rate used during the years ended December 31, 2014, 2013 and 2012, was 3.1%.
	Stock options granted by the Company subsequent to the Merger through 2011 have generally been granted with two vesting components. 50% of the option is subject to a four-year time-based schedule, and 50% of the option is subject to performance-based criteria, which also includes the requirement that the four-year time-based vesting must be satisfied. The performance-based vesting criteria is based on the performance of the Company at the Performance Target Measurement Event (a deemed liquidation, IPO or sale of the Company), as measured by the internal rate of return performance criteria ("IRR") on that date as defined in the Non-Qualified Stock Option Award Agreement under the 2010 Equity Award Plan. The Performance Target Measurement Event must occur prior to the contractual term of the options in order for the options to be subject to vesting.
	Although, the 2014 IPO was a Performance Target Measurement Event, the necessary IRR was not achieved because the Company's controlling stockholder continued to hold a significant equity position in the Company. As achieving the IRR will be based on a financing or liquidity event in the future, the Company cannot determine the probability of such an event and, therefore, has recorded no compensation expense associated with the performance-based vesting component of the options through December 31, 2014. If an employee terminates prior to the occurrence of the financing or liquidity event and has not satisfied the time-based vesting criteria (same as the vesting criteria associated with the time-based portion of the options) of the performance-based portion of the options, the employee does not retain the right to participate in any vesting related to the performance-based portion of the options. Employees who terminate and have satisfied any portion of the time-based vesting criteria of the performance-based portion of their options may continue to participate in vesting of the performance-based portion of their options for which the time-based criteria has been satisfied, up and until the termination date of the options. All stock options granted subsequent to 2011 solely vest based on a time-based vesting schedule and do not contain any performance-based vesting criteria.
	There was approximately $3,224 and $3,453 of total unrecognized compensation expense related to the performance-based vesting component of nonvested employee stock options outstanding under the Company’s stock compensation plans as of December 31, 2014, and 2013, respectively. If, prior to the option’s contractual term expiration, a financing or liquidity event occurs, that meets the performance target measurement, as defined in the underlying award agreement, and the time-based vesting component is satisfied, this expense will be recognized. As of December 31, 2014, the weighted average contractual terms of the options, subject to the performance-based vesting, was 6.25 years. The intrinsic value of the options exercised during the years ended December 31, 2014, 2013 and 2012 approximated $5,191, $2,372 and $1,276, respectively.
	Under the terms of its stock option awards, the Company permits employees to use vested shares to satisfy minimum income tax withholding requirements. In February 2013, the Company modified awards underlying options to purchase 377,312 shares of its common stock to permit the grantee to use vested shares to satisfy tax withholding requirements in excess of the minimum liability when the option is exercised. This modification resulted in the reclassification of the carrying value of these options to a liability, and the subsequent change in the fair value of the liability at each reporting period to be recorded as an expense. These outstanding stock options are remeasured at each reporting date and will continue to be remeasured until the earlier of their exercise or expiration. Any changes in valuation are recorded as stock based compensation expense for the period. As of December 31, 2013, an accrued liability of $1,910 was recorded on the Company's consolidated balance sheet. The Company recorded stock-based compensation expense of $1,292 related to changes in the fair value of the liability. All of the options subject to this modification expired in April 2014.
	Restricted Stock Units (RSUs)
On April 21, 2014, the Company’s board of directors modified the vesting terms of the 576,132 RSUs issued to certain members of senior management in May 2013 to add time-vesting criteria. The modified vesting terms provides that the RSUs will vest in two equal installments on May 21, 2015 and 2016, subject to continued employment through the applicable vesting dates. In addition, the RSUs will continue to vest on an accelerated basis upon death, disability or a change in control. The Company expects to recognize stock-based compensation expense of approximately $15.61 per share or $8,993 over the vesting period. The Company recognized stock-based compensation expense of $3,004 and $0 for the years ended December 31, 2014 and December 31, 2013 related to these awards.
Effective May 7, 2014, the Company’s board of directors approved the issuance of 188,891 RSUs to certain of the Company’s officers. The RSUs will vest in three equal installments on the first, second and third anniversary of the grant date. The Company expects to recognize stock-based compensation expense of approximately $2,833 over the vesting period of the RSU. Stock-based compensation expense recognized related to these awards was $616 for the year ended December 31, 2014.
A summary of RSU activity for the year ended December 31, 2014 is as follows:
		Unvested RSUs
Outstanding at December 31, 2013		576,132
Granted		188,891
Vested		—
Forfeited		—
Unvested at December 31, 2014		765,023

DEFINED_CONTRIBUTION_PLAN

DEFINED CONTRIBUTION PLAN	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
DEFINED CONTRIBUTION PLAN	DEFINED CONTRIBUTION PLAN
	The Company has a defined contribution plan (the "Contribution Plan") covering substantially all employees meeting certain eligibility requirements. Participants may elect to contribute a specified portion of their compensation to the Contribution Plan on a tax-deferred basis. The Company may make discretionary contributions to the Contribution Plan. The Company made contributions to the Plan of $1,458, $1,096 and $861 for the years ended December 31, 2014, 2013 and 2012, respectively.

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES
	Operating Leases
	The Company leases office space for its corporate headquarters under a non-cancelable operating lease agreement that expires in September 2016. The lease calls for initial rent payments of approximately $78 per month subject to a 3% annual escalation. The lease provides for various renewal periods. The Company also leases space for its machine shop that supports certain research, development and operational efforts, which expires in December 2016. The lease calls for rent payments of $6 per month subject to a 4% annual escalation.
	As of December 31, 2014, future minimum lease payments under the non-cancelable operating lease agreement are as follows:
		Lease
		Obligations
	Year ending December 31:
	2015	$	2,133
	2016	1,607
	2017	50
	2018	8
	2019	—
	Total minimum payments	$	3,798
	Lease for New Corporate Headquarters
	On December 11, 2014, the Company entered into a Deed of Lease (the “Lease Agreement”) with TC Oaklawn Owner, LLC (the “Landlord”) with respect to the Company’s new corporate headquarters to be located in two adjacent buildings in Leesburg, Virginia (the “Buildings”). The Company has agreed to, among other items, lease the entire rentable space of the Buildings, containing a total of approximately 145,819 square feet, for an initial term of 186 calendar months. The term of the lease will commence approximately five months after the Landlord completes the base building improvements, which is expected to be in February 2016. Under the terms of the Lease Agreement, upon the commencement of the lease term, the Company will (subject to an initial abatement described below) pay to the Landlord an annual base rent of approximately $3,201, which will increase by 2.50% per year (without regard to the initial abatement) commencing upon the first anniversary of the commencement of the lease term. The Landlord will abate the first six months of the base rent after the commencement of the lease term. The Company will bear the cost for real estate taxes, utilities, maintenance, repairs and insurance.
	The Company provided a security deposit in the form of an uncollaterized letter of a credit in the amount of $6,000, which letter of credit may be reduced from time to time upon the satisfaction of certain conditions as set forth in the Lease Agreement.
	The Landlord will provide a tenant improvement allowance to the Company for the construction of certain improvements to the Buildings. The Company is required to fund all actual costs of tenant improvements in excess of Landlord’s tenant improvement allowance and currently expects to spend at least $6,667 on tenant improvements in excess of the Landlord’s tenant improvement allowance, which has been placed in an escrow account and reflected on the accompanying balance sheet in Other Assets as of December 31, 2014.
	As of December 31, 2014, minimum lease payments under the lease agreement assuming a lease commencement date in February 2016 are $1,337 in 2016; $3,282 in 2017; $3,364 in 2018; $3,448 in 2019 and 46,427 in 2020 and thereafter.
	Intellectual Property
	In the normal course of business, the Company enters into agreements to obtain the rights to certain intellectual property. These agreements may require an up-front payment, milestone payments and/or royalties. Typically, the Company has certain rights to cancel these agreements, with notice, without additional payments due other than the amount due at the time of cancellation. As of December 31, 2014, the aggregate amount of these future payments, assuming achievement of applicable milestones and non-cancellation, was $1,613 over a period not less than five years. Royalties ranging from 2% to 10% of net sales may be due on the sales of related products. Some of the agreements contain minimum annual royalty amounts.
	In November 2011, the Company entered into an agreement to purchase certain proprietary technology which could require it to make additional aggregate payments of up to $13,350 should certain milestones be met, including milestones related to regulatory applications and approvals. Cumulative payments under this agreement totaled $100 through December 31, 2014. During 2014 and 2013, the Company made no additional payments. 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. A royalty payment of 7% of net sales of related products may be due until such sales reaches $20,000. The product related to this agreement has not yet been commercialized.
	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. The Company is not aware of any pending or threatened legal proceeding against it that the Company expects would have a material adverse effect on its business, operating results or financial condition. However, the Company is a party in multiple legal actions involving claimants seeking various remedies, including monetary damages, and none of the outcomes are certain or entirely within the Company's control.

RELATED_PARTIES

RELATED PARTIES	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
RELATED PARTIES	RELATED PARTIES
	In connection with the Merger, the Company and K2M entered into a management agreement with the major stockholder of the Company. Fees paid for such agreement totaled $372, $775 and $500 for the years ended December 31, 2014, 2013 and 2012, respectively. The Company records such costs in general and administrative expense in its consolidated statements of operations. The management agreement was terminated in May 2014 following the Company's IPO.
	In connection with the IPO, certain stockholders of the Company granted the underwriters an option to purchase from such selling shareholders additional shares of common stock at the public offering price, less underwriting discounts.   On June 10, 2014, the underwriters exercised this option and purchased 1,000,000 shares of common stock from selling shareholders at a price of $15 per share before underwriting discounts.  The Company received no proceeds from the sale of these shares.

INCOME_TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES
	The following table summarizes the loss before benefit from income taxes:
		Year Ended
		December 31,
		2014				2013				2012
	United States	$	(45,392	)		$	(37,884	)		$	(40,344	)
	Foreign	(14,359		)		(8,370		)		(5,352		)
	Total	$	(59,751	)		$	(46,254	)		$	(45,696	)
	The benefit from income taxes is as follows:
		Year Ended
		December 31,
		2014				2013				2012
	Current:
	Federal	$	—			$	—			$	—
	State	105				80				74
	Foreign	—				71				80
	Deferred:
	Federal	(16,636		)		(12,590		)		(12,396		)
	State	(975		)		(1,969		)		(1,583		)
	Foreign	(3,042		)		(1,681		)		(1,575		)
	Change in valuation allowance	20,434				7,748				2,359
	Income tax benefit	$	(114	)		$	(8,341	)		$	(13,041	)
	The Company’s net deferred liability consists of the following:
		December 31,
		2014				2013
	Net operating loss (NOL) carryforwards	$	24,697			$	13,322
	Research and development and alternative minimum tax (AMT) credit carryforward	1,907				1,443
	Inventory	6,703				6,481
	Stock-based compensation	4,456				3,254
	Intellectual property agreements	3,227				4,303
	Other deferred temporary differences	3,717				2,989
	Intangible assets	(14,797		)		(22,534		)
	Valuation allowance	(34,952		)		(14,518		)
	Net deferred tax liability	$	(5,042	)		$	(5,260	)
	Approximately $6,045 of the NOL carryforward of $24,697 for the year ended December 31, 2014, is related to operations outside the United States and does not expire. The remaining NOL starts to expire in 2019. Tax credit carryforwards of $1,907 begin to expire in 2027. Under Section 382 of the Internal Revenue Code of 1986, as amended (the "IRC"), certain significant changes in ownership may restrict the future utilization of the Company's tax loss carry forwards and tax credit carry forwards.
	The following table summarizes a reconciliation of the U.S. statutory federal income tax rate to the Company’s effective tax rate, as a percentage of loss before income tax benefit for the years ended December 31, 2014, 2013 and 2012:
		Year Ended
		December 31,
		2014			2013			2012
	Federal tax at statutory rates	34	%		34	%		34	%
	State taxes, net of federal benefit	2.3			2.3			2.3
	Tax credits	0.6			0.5			—
	Permanent difference	1.7			0.1			0.1
	Foreign income taxes	(2.0	)		(1.8	)		(1.0	)
	Change in valuation allowance	(34.2	)		(16.8	)		(5.3	)
	Tax rate adjustment and other	(2.2	)		(0.3	)		(1.6	)
	Income tax benefit	0.2	%		18	%		28.5	%
	The following reflects a rollforward of the deferred tax asset valuation allowance for the years ended December 31, 2014, 2013 and 2012:
		Year Ended
		December 31,
		2014				2013				2012
	Beginning	$	(14,518	)		$	(6,770	)		$	(4,411	)
	Increase to allowance	(20,434		)		(7,748		)		(2,359		)
	Decrease to allowance	—				—				—
	Ending	$	(34,952	)		$	(14,518	)		$	(6,770	)
	The Company is subject to income taxes in the United States and certain foreign jurisdictions. Significant judgment is required in determining the consolidated provision for income taxes and recording the related deferred tax assets and liabilities. In the ordinary course of business, there are transactions and calculations where the ultimate tax determination is uncertain.
	As of December 31, 2014 and 2013, the Company had no uncertain tax positions. The Company’s returns are not currently under examination by the Internal Revenue Service or other taxing authorities. The Company is subject to income tax examinations for its U.S federal tax returns and foreign examinations for years 2011 and subsequent; and U.S., state and local returns for years 2010 and subsequent. Although the Company believes that the estimates and assumptions supporting its tax positions are reasonable, the final determination of tax audits and any related litigation could be materially different from that which is reflected in historical income tax provisions and recorded assets and liabilities. Based on the results of an audit or litigation, there could be a material effect on the Company’s benefit from income taxes, net loss or cash flows in the period or periods for which that determination is made.

NET_LOSS_PER_SHARE

NET LOSS PER SHARE	12 Months Ended
	Dec. 31, 2014
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 the Company’s common stockholders:
		Year Ended
		December 31,
		2014				2013			2012
	Net loss per common share:
	Net loss	$	(59,637	)		$	(37,913	)	$	(32,655	)
	Less: accretion and adjustment of Series A Preferred and Series B Preferred	6,879				(19,439		)	(9,954		)
	Net loss attributable to common stockholders	$	(52,758	)		$	(57,352	)	$	(42,609	)
	Basic and diluted loss per common share
	Basic and diluted weighted average common shares outstanding	31,887,246				22,238,632			21,920,512
	Basic and diluted loss per common share	$	(1.65	)		$	(2.58	)	$	(1.94	)
	Diluted loss per share for the years ended December 31, 2014, 2013 and 2012 does not reflect the following weighted average potential common shares, as the effect would be antidilutive:
		Year Ended
		December 31,
		2014			2013			2012
	Series A Preferred and Series B Preferred	—			5,576,955			4,326,853
	Stock options	4,277,229			4,179,119			4,659,470
	Restricted stock units	765,023			576,132			—

SEGMENT_AND_GEOGRAPHICAL_CONCE

SEGMENT AND GEOGRAPHICAL CONCENTRATION	12 Months Ended
	Dec. 31, 2014
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. The Company globally manages the business 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 28.7% of total revenue for the year ended December 31, 2014; however, revenue earned in any individual foreign country is below 10% of the Company’s consolidated revenue.
	The following table represents total revenue by geographic area, based on the location of the customer:
		Year Ended
		December 31,
		2014		2013		2012
	United States	$	133,110	$	111,772	$	99,845
	International	53,562		45,812		35,300
	Total	$	186,672	$	157,584	$	135,145
	The Company classifies sales within the United States into three categories: complex spine pathologies, minimally invasive procedures and degenerative and other conditions. A significant portion of the Company’s international revenue is derived from the Company’s distributor partners who do not report their product usage at the surgeon or hospital level, which prevents the Company from providing a specific breakdown for its international revenue among its three product categories. These sales transactions are settled when the Company ships the product to the agent.
	The following table represents domestic revenue by procedure category. To further align its procedure categorizations, beginning in the second quarter of 2014, the Company began to report MIS sales attributable to complex spine procedures, which were historically reported in the minimally invasive category, within the complex spine category.  Accordingly, the complex spine category presented below includes MIS sales attributable to complex spine procedures of $5,937 and $4,905 for the years ended December 31, 2013 and 2012, respectively, which was historically reported in the minimally invasive category.
		Year Ended
		December 31,
		2014		2013		2012
	Complex spine	$	54,030	$	46,442	$	42,697
	Minimally invasive	20,670		18,403		16,766
	Degenerative	58,410		46,927		40,382
		133,110		111,772		99,845
	International	53,562		45,812		35,300
	Total	$	186,672	$	157,584	$	135,145
	The following table represents long-lived assets (1) by geographic area:
		December 31,
		2014		2013
	United States	$	23,684	$	15,454
	International	1,928		2,795
	Total	$	25,612	$	18,249
	(1) Long-lived assets includes property and equipment and surgical instruments included in other assets.

RECENT_ACCOUNTING_PRONOUNCEMEN

RECENT ACCOUNTING PRONOUNCEMENTS	12 Months Ended
	Dec. 31, 2014
Accounting Changes and Error Corrections [Abstract]
RECENT ACCOUNTING PRONOUNCEMENTS	RECENT ACCOUNTING PRONOUNCEMENTS
	The Company qualifies as an “emerging growth company” ("EGC") pursuant to the provisions of the JOBS Act and has elected to take advantage of the extended transition period provided in Section 7(a)(2)(B) of the Securities Act which permits EGCs to defer compliance with new or revised accounting standards (the "EGC extension") until non-issuers are required to comply with such standards. Accordingly, so long as the Company continues to qualify as an EGC, it will not have to adopt or comply with new accounting standards until non-issuers are required to comply with such standards.
	In March 2013, the FASB issued guidance clarifying the accounting for the release of cumulative translation adjustment into net income when a parent either sells part or all of its investment in a foreign entity or no longer holds a controlling interest in a subsidiary or group of assets that is a nonprofit or a business within a foreign entity. For public entities that do not qualify for the EGC extension, the new guidance is effective prospectively for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2013. For EGCs that have elected the EGC extension including the Company, and non-public issuers, the guidance is effective prospectively for the first annual period beginning after December 15, 2014, and interim and annual periods thereafter. Early adoption is permitted. The Company does not anticipate that this adoption will have a material impact on its financial position, results of operations or cash flows.
	In July 2013, the FASB issued new guidance on the financial statement presentation of unrecognized tax benefits when a net operating loss carryforward, a similar tax loss, or a tax credit carryforward exists. For public entities that do not qualify for the EGC extension, the guidance was effective for fiscal years and interim periods within those years, beginning after December 15, 2013 and may be applied retrospectively. EGCs that have elected the EGC extension, including the Company, and non-public issuers will be required to comply with the guidance on a prospective basis in the first quarter of 2015. Early adoption is permitted. Although adoption of this new guidance may impact how such items are classified on the Company’s balance sheet, such change is not expected to be material. There will be no changes in the presentations of the Company’s other financial statements
	In May 2014, the FASB amended the existing accounting standards for revenue recognition. The amendments are based on the principle that revenue should be recognized to depict the transfer of goods and services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods and services. For public entities other than EGCs that have elected the EGC extension, the guidance will be effective for annual reporting periods beginning after December 15, 2016. EGCs that have elected the EGC extension, including the Company, and non-public entities will be required to comply with the guidance for annual reporting periods beginning after December 15, 2017. Early adoption is not permitted. The amendments may be applied retrospectively to each prior period presented or retrospectively with the cumulative effect recognized as of the date of the initial application. The Company is evaluating the impact of these amendments and the transition alternatives on its consolidated financial statements.

QUARTERLY_FINANCIAL_DATA_UNAUD

QUARTERLY FINANCIAL DATA (UNAUDITED)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
QUARTERLY FINANCIAL DATA (UNAUDITED)	QUARTERLY FINANCIAL DATA (UNAUDITED)
	The following tables summarize the unaudited quarterly statements of operations for the Company for 2014 and 2013. The tables include all necessary adjustments, consisting only of normal recurring adjustments necessary in the opinion of management for a fair statement of the results for interim periods.
		31-Dec-14			30-Sep-14			30-Jun-14			31-Mar-14
	Revenue	$	49,309		$	47,624		$	47,488		$	42,251
	Gross profit	33,092			31,489			31,454			27,837
	Loss from operations	(8,552		)	(12,906		)	(12,813		)	(13,698		)
	Net loss	(11,067		)	(16,140		)	(17,683		)	(14,747		)
	Net loss per common share	(0.30		)	(0.43		)	(0.32		)	(0.71		)
		31-Dec-13			30-Sep-13			30-Jun-13			31-Mar-13
	Revenue	$	42,609		$	39,776		$	40,101		$	35,098
	Gross profit	27,339			27,994			27,711			24,378
	Loss from operations	(12,667		)	(9,559		)	(10,956		)	(11,739		)
	Net loss	(11,972		)	(6,178		)	(8,884		)	(10,879		)
	Net loss per common share	(0.79		)	(0.28		)	(0.43		)	(1.09		)

SUBSEQUENT_EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2014
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS
	On February 2, 2015, the Company completed a follow-on offering of 6,044,990 shares of its common stock at a price of $18.75 per share.  The Company sold 2,044,990 shares of common stock in the offering and selling stockholders sold 4,000,000 shares of common stock in the offering. The Company received net proceeds from the offering of approximately $35,900, after deducting the underwriting discount and estimated offering expenses.
	The proceeds of the primary portion of the offering will be used by the Company for working capital and general corporate purposes which is expected to include the expansion of the Company's global distribution network and the purchase of inventory to support sales efforts. Use of proceeds may also include the acquisition of or investment in complementary products, technologies or businesses. The principal purposes of the secondary offering were to facilitate an orderly distribution of shares by the selling stockholders and to increase the public float of the Company's shares. The Company did not receive any proceeds from shares of common stock sold by the selling stockholders.
	In connection with the offering, certain of the selling stockholders granted the underwriters an option to purchase from them additional shares of common stock at the public offering price, less underwriting discounts.  On February 12, 2015, the underwriters exercised this option and purchased 906,748 shares of common stock from the selling stockholders at a price of $18.75 per share before underwriting discounts.  The Company received no proceeds from the sale of these shares.

GENERAL_AND_SUMMARY_OF_SIGNIFI1

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - (Policies)	12 Months Ended
	Dec. 31, 2014
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 (US GAAP) 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 revenue and expenses during the reporting period. Actual results could differ from those estimates.
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 the Company’s stock option grants (see Note 10) and the if-converted method is used to determine the dilutive effect of the Company’s Series A Preferred and the Series B Preferred (see Note 9). 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.
Foreign Currency Translation and Other Comprehensive Loss	Foreign Currency Translation and Other Comprehensive Loss
	The account balances of foreign subsidiaries are translated into U.S. dollars using exchange rates for assets and liabilities at the balance sheet date and average prevailing exchange rates for the period for revenue and expense accounts. Adjustments resulting from translation are included in other comprehensive income (loss), which is the Company’s only component of accumulated comprehensive income (loss).
	Remeasurement gains and losses from foreign currency transactions are included in other expense, net within the consolidated statements of operations in the period in which they occur.
Cash and Cash Equivalents	Cash and Cash Equivalents
	The Company considers all highly liquid investments with a maturity of three months or less when purchased to be cash equivalents.
Restricted Cash	Restricted Cash
	The Company classifies cash as restricted when cash is unavailable for withdrawal or usage. Restrictions may include legally restricted deposits, contract bids or contracts entered into with others, or the Company’s statements of intention with regard to particular deposits.
Accounts Receivable	Accounts Receivable
	Accounts receivable are reported in the consolidated balance sheets at outstanding amounts, less the allowance for doubtful accounts. The Company performs ongoing credit evaluations of certain customers and generally extends credit without requiring collateral. The Company periodically assesses the collectability of accounts receivable considering factors such as the specific evaluation of collectability, historical collection experience and economic conditions in individual markets and records an allowance for doubtful accounts for the estimated uncollectible amount as appropriate.
Inventory	Inventory
	Inventory consists primarily of finished goods and surgical instruments available for sale and is stated at the lower of cost or market using a weighted-average cost method. The Company reviews its inventory on a periodic basis for excess, obsolete, and impaired inventory and records a reserve for the identified items.
Property and Equipment	Property and Equipment
	Property and equipment are stated at cost net of accumulated depreciation and amortization. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts, and any resulting gain or loss is credited or charged to the consolidated statements of operations. Repairs and maintenance costs are expensed as incurred.
	Depreciation of property and equipment is computed using the straight-line method over the estimated useful lives of the respective assets. Amortization of leasehold improvements is recorded over the shorter of the life of the improvement or the remaining term of the lease using the straight-line method.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets
	Goodwill represents the excess of the consideration transferred over the estimated fair value of assets acquired and liabilities assumed in connection with the Merger.
	Goodwill and indefinite lived intangible assets are not amortized but are evaluated annually or more frequently for impairment if impairment indicators exist. Such indicators include, but are not limited to (i) a significant adverse change in the business climate or environment, (ii) unanticipated competition, or (iii) adverse action or assessment by a regulator. The Company’s annual impairment date is November 1. The Company concluded it has one reporting unit. Prior to performing the annual two-step goodwill impairment test, the Company is first permitted to perform a qualitative assessment to determine if the two-step quantitative test must be completed. The qualitative assessment considers events and circumstances such as macroeconomic conditions, industry and market conditions, cost factors and overall financial performance, as well as company and specific reporting unit specifications. If after performing this assessment, the company concludes it is more likely than not that the fair value of a reporting unit is less than its carrying amount, then it is required to perform a two-step quantitative test. Otherwise, the two-step test is not required. In the first step of the quantitative test, the company is required to determine the fair value of the reporting unit and compare it to the carrying amount of the reporting unit. Fair value of the reporting unit is determined using a discounted cash flow valuation. Determining the fair value of the reporting unit is judgmental in nature and involves the use of significant estimates and assumptions. These estimates and assumptions include changes in revenue and operating margins used to project future cash flows, discount rates, and future economic and market conditions. If the carrying amount of the reporting unit exceeds the fair value of the reporting unit, the company performs the second step of the impairment test, as this is an indication that the reporting unit goodwill may be impaired. In the second step of the impairment test, the company determines the implied fair value of the reporting unit’s goodwill. If the carrying value of a reporting unit’s goodwill exceeds its implied fair value, then an impairment of goodwill has occurred and the company must recognize an impairment loss for the difference between the carrying amount and the implied fair value of goodwill.
	The Company used a qualitative assessment for its goodwill impairment testing for 2014 and 2013, and a quantitative assessment for its goodwill for such testing in 2012. The Company’s evaluation of goodwill completed during the years ended December 31, 2014, 2013 and 2012 resulted in no impairment losses.
	The Company’s indefinite-lived intangible assets include trademarks and purchased in-process research and development (IPR&D) projects, which originated from the merger and were measured at their respective estimated fair values as of the acquisition date.
	The Company used a qualitative assessment for its indefinite lived intangible asset impairment testing. The Company’s evaluation of indefinite-lived intangible assets evaluation completed during the years ended December 31, 2014, 2013 and 2012 resulted in no impairment losses.
	Finite-lived intangible assets include licensed technology, developed technology, and customer relationships and are amortized over estimated useful lives, which range from four–seven years. The Company recorded no impairment loss during the years ended December 31, 2014, 2013 and 2012.
Other Assets	Other Assets
	Other long-term assets consist mainly of surgical instruments used primarily in the domestic and direct international distribution channels to implant the Company’s products. Surgical instruments are stated at cost less accumulated amortization. The Company amortizes these instruments to cost of revenues over their estimated useful life.
	The Company provides surgical instruments to its customers for use to implant its products during a surgical procedure. Following completion of the procedure, the instruments are returned to the Company upon which it will sanitize the instrument and provide it to another customer.
	As a result of the completion of an extensive evaluation of the useful life of surgical instruments in 2013, including consideration of the average age of instruments on-hand and the average age of instruments when disposed of, the Company determined that the estimated useful life of such instruments had increased to five years, from three years as previously estimated. The Company accounted for this change in the estimated useful life beginning January 1, 2013.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets
	Long-lived assets, such as fixed assets and other finite-lived intangible assets are reviewed for impairment whenever circumstances indicate that the carrying amount of the asset may not be recoverable. The carrying amount of a long-lived asset may not be recoverable if it exceeds the sum of undiscounted cash flows expected to be generated by the asset. If an asset is determined to be impaired, the loss is measured as the amount by which the carrying amount of the asset exceeds its estimated fair value. Considerable management judgment is necessary to estimate undiscounted future cash flows. Accordingly, actual results could differ from such estimates. No events have been identified that caused an evaluation of the recoverability of the long-lived assets.
Fair Value Measurements	Fair Value Measurements
	Fair value is defined in the fair value measurement accounting guidance as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date, or exit price. Assets and liabilities subject to fair value measurements are required to be disclosed within a specified fair value hierarchy. The fair value hierarchy ranks the quality and reliability of inputs or assumptions used in the determination of fair value and requires assets and liabilities carried at fair value to be classified and disclosed in one of the following categories based on the lowest level input used that is significant to a particular fair value measurement:
	•Level 1 – Defined as observable inputs such as unadjusted quoted prices in active markets for identical assets.
	•Level 2 – Defined as observable inputs other than Level 1 prices, such as quoted prices for similar assets, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.
	•Level 3 – Defined as unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions.
	The Company’s cash and cash equivalents are subject to fair value measurements. In accordance with the hierarchy, the inputs used in measuring the fair value of the cash equivalents are considered to be Level 1.
	The Company’s merger was consummated on August 12, 2010. Changes in the fair value of the contingent consideration liability resulted from either the passage of time or events occurring after the acquisition date, such as changes in the estimate of the probability of recording the Core Business Revenues. The fair value of the contingent consideration (Level 3) was measured based on the present value of the consideration expected to be  transferred using a discounted cash flow analysis. The discount rate is a significant unobservable input in such present value computations. Discount rates ranged between 15.0% and 17.5% depending on the risk associated with the cash  flows.
	The Company applies the fair value measurement accounting guidance to nonfinancial assets upon the acquisition of businesses or in conjunction with the measurement of an impairment loss of a long-lived asset, goodwill or other intangible asset under the accounting guidance for impairments.
Financial Instruments	The Company considers the recorded costs of certain financial assets and liabilities, including cash and cash equivalents, accounts receivable, accounts payable and accrued expenses, to approximate their fair value because of relatively short maturities at December 31, 2014 and December 31, 2013. The fair values of the bank line of credit and other long-term liabilities approximated their carrying amounts as of December 31, 2014 and December 31, 2013, based on rates and terms available to the Company at that time.
Concentration of Credit Risk	Financial instruments that potentially subject the Company to a concentration of credit risk consist principally of cash and cash equivalents and accounts receivable. The Company maintains its cash balances with creditworthy financial institutions in the United States, and the balances may exceed, at times, the amount insured by the Federal Deposit Insurance Corporation. No single customer represented more than 10% of revenue for any period presented.
Revenue Recognition	Revenue Recognition
	Revenue is recognized when all of the following criteria are met: persuasive evidence of an arrangement exists, delivery has occurred or service has been rendered, the price to the buyer is fixed or determinable, and collectability is reasonably assured.
	The Company’s revenue in its direct markets is generated by making its products available to hospitals that purchase specific products for use in surgery on a case-by-case basis. Revenue from sales generated by use of products is recognized upon receipt of a delivered order confirming that the Company’s products have been used in a surgical procedure.
	International sales outside of its direct markets are transacted with independent distributors, who then resell the products to their hospital customers. The Company recognizes revenue upon shipment of its products to the international distributors, who accept title at point of shipment.
Shipping and Handling Costs	Shipping and Handling Costs
	Shipping and handling costs are charged to sales and marketing expense in the consolidated statements of operations
Research, Development, and Engineering	Research, Development, and Engineering
	The Company expenses its research, development and engineering costs as incurred.
Stock-Based Compensation	Stock-Based Compensation
	The Company awards stock-based compensation primarily in the form of stock options and restricted stock units (RSUs). For stock options awarded, stock-based compensation is based on the fair value of such awards granted to employees using the Black-Scholes-Merton option pricing model and is expensed on a straight-line basis over the award's vesting period, less awards expected to be forfeited using estimated forfeiture rates.
	For RSUs awarded after the Company's IPO, the stock-based compensation is based on the closing market share price of the Company's common stock on the date of award and is expensed on a straight-line basis over the award's vesting period.
	The Company also recognizes stock-based compensation for participation in its 2014 Employee Stock Purchase Plan ("ESPP"). The ESPP provides for a look-back option feature that gives an option to the participant to purchase the Company's common stock at a discount to the market price for such stock. The ESPP is compensatory to the Company. The compensation costs are recognized over the offering period based on the fair value of the option granted to participants and the number of shares expected to be purchased at the end of the offering period.
Income Taxes	Income Taxes
	The Company accounts for income taxes using the liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities, their respective tax bases and operating loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the year in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in operations in the period that includes the enactment date.
	Valuation allowances are established when necessary to reduce net deferred tax assets to the amount expected to be realized. Income tax expense (benefit) is the tax payable (receivable) for the period and the change during the period in deferred tax assets and liabilities.
	As prescribed by the accounting guidance, the Company uses a more-likely-than-not recognition threshold based on the technical merits of the tax position taken. Tax positions that meet the more-likely-than-not recognition threshold are measured at the largest amount of the tax benefits, as determined on a cumulative probability basis, that are more-likely-than-not to be realized upon ultimate settlement in the financial statements. The Company recognizes interest and penalties related to income tax matters in income tax expense (benefit).
Redeemable Convertible Preferred Stock	Redeemable Convertible Preferred Stock
	The Company used the effective interest method to accrete the differences between the carrying value and the estimated redemption value of its preferred stock, such that the carrying value approximated the redemption value on the earliest possible redemption date.
Recent Accounting Pronouncements	RECENT ACCOUNTING PRONOUNCEMENTS
	The Company qualifies as an “emerging growth company” ("EGC") pursuant to the provisions of the JOBS Act and has elected to take advantage of the extended transition period provided in Section 7(a)(2)(B) of the Securities Act which permits EGCs to defer compliance with new or revised accounting standards (the "EGC extension") until non-issuers are required to comply with such standards. Accordingly, so long as the Company continues to qualify as an EGC, it will not have to adopt or comply with new accounting standards until non-issuers are required to comply with such standards.
	In March 2013, the FASB issued guidance clarifying the accounting for the release of cumulative translation adjustment into net income when a parent either sells part or all of its investment in a foreign entity or no longer holds a controlling interest in a subsidiary or group of assets that is a nonprofit or a business within a foreign entity. For public entities that do not qualify for the EGC extension, the new guidance is effective prospectively for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2013. For EGCs that have elected the EGC extension including the Company, and non-public issuers, the guidance is effective prospectively for the first annual period beginning after December 15, 2014, and interim and annual periods thereafter. Early adoption is permitted. The Company does not anticipate that this adoption will have a material impact on its financial position, results of operations or cash flows.
	In July 2013, the FASB issued new guidance on the financial statement presentation of unrecognized tax benefits when a net operating loss carryforward, a similar tax loss, or a tax credit carryforward exists. For public entities that do not qualify for the EGC extension, the guidance was effective for fiscal years and interim periods within those years, beginning after December 15, 2013 and may be applied retrospectively. EGCs that have elected the EGC extension, including the Company, and non-public issuers will be required to comply with the guidance on a prospective basis in the first quarter of 2015. Early adoption is permitted. Although adoption of this new guidance may impact how such items are classified on the Company’s balance sheet, such change is not expected to be material. There will be no changes in the presentations of the Company’s other financial statements
	In May 2014, the FASB amended the existing accounting standards for revenue recognition. The amendments are based on the principle that revenue should be recognized to depict the transfer of goods and services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods and services. For public entities other than EGCs that have elected the EGC extension, the guidance will be effective for annual reporting periods beginning after December 15, 2016. EGCs that have elected the EGC extension, including the Company, and non-public entities will be required to comply with the guidance for annual reporting periods beginning after December 15, 2017. Early adoption is not permitted. The amendments may be applied retrospectively to each prior period presented or retrospectively with the cumulative effect recognized as of the date of the initial application. The Company is evaluating the impact of these amendments and the transition alternatives on its consolidated financial statements.

GENERAL_AND_SUMMARY_OF_SIGNIFI2

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Schedule of impact to consolidated results of operations due to change in estimated useful life	This change had the effect of reducing cost of revenue, net loss, net loss attributable to common stockholders and net loss per share in its consolidated results of operations as follows:
		Year Ended
		December 31,
		2014		2013
	Cost of revenue	$	4,827	$	6,732
	Net loss	$	4,817	$	5,520
	Net loss attributable to common stockholders	$	4,817	$	5,520
	Net loss per share (basic and diluted)	$	0.15	$	0.25

ACCOUNTS_RECEIVABLE_Tables

ACCOUNTS RECEIVABLE - (Tables)	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Schedule of Accounts Receivable	Receivables consist of the following:
		December 31,
		2014			2013
	Accounts receivable	$	36,431		$	35,271
	Allowances	(2,494		)	(2,447		)
	Accounts receivable, net	$	33,937		$	32,824
	The following reflects a rollforward of the accounts receivable allowances for the years ended December 31, 2014, 2013 and 2012:
		December 31,
		2014			2013			2012
	Beginning	$	(2,447	)	$	(2,217	)	$	(2,020	)
	Additions	(436		)	(230		)	(383		)
	Write-offs	389			—			186
	Ending	$	(2,494	)	$	(2,447	)	$	(2,217	)

INVENTORY_Tables

INVENTORY - (Tables)	12 Months Ended
	Dec. 31, 2014
Inventory Disclosure [Abstract]
Schedule of Current Inventory
		December 31,
		2014			2013
	Finished goods	$	78,331		$	64,539
	Inventory allowances	(25,714		)	(25,316		)
	Inventory, net	$	52,617		$	39,223

PROPERTY_AND_EQUIPMENT_Tables

PROPERTY AND EQUIPMENT - (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and equipment consist of the following:
		Estimated	December 31,
		Useful Lives	2014		2013
	Equipment	3 years	2,725		2,412
	Software	3 years	3,923		2,376
	Computer equipment	3 years	1,445		1,265
	Leasehold improvements	Various	1,109		1,098
	Furniture and office equipment	5 years	1,048		673
	Vehicles and other	Various	458		12
	Total		10,708		7,836
	Less accumulated depreciation and amortization		(6,488	)	(4,858	)
	Property and equipment, net		4,220		2,978

GOODWILL_AND_INTANGIBLE_ASSETS1

GOODWILL AND INTANGIBLE ASSETS - (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets and Goodwill	Goodwill and intangible assets comprise of the following:
		As of December 31, 2014
		Estimated		Gross		Accumulated			Net
		Useful Lives				Amortization
	Goodwill	—		$	121,814	$	—		$	121,814
	Indefinite-lived intangible assets:
	Trademarks			12,900		—			12,900
	In-process research and development (1)	—		900		—			900
	Other	—		278		—			278
	Subtotal			14,078		—			14,078
	Subject to amortization
	Developed technology (1)	4 - 6 years		62,000		(46,460		)	15,540
	Licensed technology	4 - 6 years		52,600		(52,175		)	425
	Customer relationships	4 - 7 years		29,700		(18,563		)	11,137
	Patents and other	2 - 17 years		1,414		(985		)	429
	Subtotal			145,714		(118,183		)	27,531
	Total			$	281,606	$	(118,183	)	$	163,423
		As of December 31, 2013
		Estimated		Gross		Accumulated			Net
		Useful Lives				Amortization
	Goodwill	—		$	121,814	$	—		$	121,814
	Indefinite-lived intangible assets:
	Trademarks	—		12,900		—			12,900
	In-process research and development (1)	—		1,500		—			1,500
	Other	—		296		—			296
	Subtotal			14,696		—			14,696
	Subject to amortization
	Developed technology (1)	4 - 6 years		61,600		(36,466		)	25,134
	Licensed technology	4 - 6 years		52,600		(43,947		)	8,653
	Customer relationships	4 - 7 years		29,700		(14,320		)	15,380
	Patents and other	2 - 17 years		1,313		(720		)	593
	Subtotal			145,213		(95,453		)	49,760
	Total			$	281,723	$	(95,453	)	$	186,270
Schedule of Expected Amortization Expense	As of December 31, 2014, the expected amortization expense for each of the next five years and thereafter is as follows:
	2015	$	10,275
	2016	10,205
	2017	6,590
	2018	95
	2019 and thereafter	366
	Total	$	27,531

OTHER_ASSETS_Tables

OTHER ASSETS - (Tables)	12 Months Ended
	Dec. 31, 2014
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Other Assets	Other assets comprises the following:
		December 31,
		2014		2013
	Surgical instruments, net	$	21,392	$	15,271
	Restricted cash	8,114		—
	Other	166		143
	Total	$	29,672	$	15,414

ACCRUED_EXPENSES_Tables

ACCRUED EXPENSES - (Tables)	12 Months Ended
	Dec. 31, 2014
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following:
		December 31,
		2014		2013
	Accrued commissions	$	4,942	$	2,837
	Accrued royalties	2,464		2,230
	Stock option awards liability	—		2,076
	Other	2,671		1,617
	Total	$	10,077	$	8,760

DEBT_Tables

DEBT - (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Schedule of Debt	Debt consists of the following:
		December 31,
		2014		2013
	Bank line of credit	$	—	$	23,500
	Notes to stockholders	—		22,270
	Total debt	—		45,770
	Less unamortized discounts	—		(2,620		)
	Debt, net of discounts	$	—	$	43,150

PREFERRED_STOCK_Tables

PREFERRED STOCK - (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Schedule of Activity in Series A and B Convertible Preferred Stock	The following is a rollforward of activity in the Series A Preferred and Series B Preferred accounts during the years ended December 31, 2012, 2013 and 2014, respectively.
		Series A Preferred							Series B Preferred
		Shares							Shares
		Authorized		Outstanding		Amount			Authorized		Outstanding		Amount
	Balance at December 31, 2011	7,300,000		7,250,885		$	45,793		5,249,000		2,624,672		$	19,926
	Issuance of preferred stock	—		—		—			—		638,696		2,433
	Issuance costs of preferred stock	—		—		—			—		—		(38		)
	Accretion of preferred stock to fair value	—		—		4,732			—		—		5,222
	Balance at December 31, 2012	7,300,000		7,250,885		50,525			5,249,000		3,263,368		27,543
	Issuance of preferred stock	—		—		—			1,251,000		3,037,922		11,574
	Accretion of preferred stock to fair value	—		—		6,142			—		—		13,297
	Balance at December 31, 2013	7,300,000		7,250,885		56,667			6,500,000		6,301,290		52,414
	Payment of dividend	—				(11,932		)					(6,615		)
	Accretion of preferred stock to fair value	—		—		1,195			—		—		(15		)
	Adjustment of preferred stock to fair value prior to conversion	—		—		(1,170		)	—		—		(6,889		)
	Conversion to common stock	(7,300,000	)	(7,250,885	)	(44,760		)	(6,500,000	)	(6,301,290	)	(38,895		)
	Balance at December 31, 2014	—		—		$	—		—		—		$	—

STOCKBASED_COMPENSATION_Tables

STOCK-BASED COMPENSATION - (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of stock-based compensation expense	The Company recognized the following stock-based compensation expense related to stock options issued to employees and non-employees and RSUs issued to employees which is inclusive of the amounts detailed below:
			Year Ended
			December 31,
			2014 (1)			2013 (1)				2012 (1)
	Cost of revenue		$	424		$	532			$	32
	Research, development, and engineering		439			92				136
	Sales and marketing		2,146			889				696
	General and administrative		2,798			1,366				1,379
			$	5,807		$	2,879			$	2,243
	Employees		$	5,537		$	2,664			$	2,195
	Non-employees		270			215				48
	Total		$	5,807		$	2,879			$	2,243
	-1	Stock-based compensation expense included $0, $1,291 and $0 related to stock option liability awards for the year ended December 31, 2014, 2013 and 2012, respectively.
Schedule of employee stock option plan activity	A summary of stock option plans activity during the year ended December 31, 2014 is as follows:
			Shares		Weighted-				Weighted-		Aggregate
					Average				Average		Intrinsic
					Exercise				Remaining		Value (1)
					Price				Contractual
									Term
									(years)
	Outstanding at December 31, 2013		4,179,119		$	8.18			5.64		$	31,434
	Granted		707,796		15.04
	Exercised		(512,933	)	6.1
	Expired		(31,888	)	4.41
	Forfeited		(64,865	)	10.9
	Outstanding at December 31, 2014(2)		4,277,229		$	9.55			5.83		$	48,418
	Vested or expected to vest:
	At December 31, 2014(3)		4,102,613		$	9.51			5.78		$	46,595
	Vested:
	At December 31, 2014		2,302,735		$	7.93			4.44		$	29,797
	-1	Calculated using the estimated fair market value per share of the Company’s common stock as on December 31, 2014 and actual per share fair market value at December 31, 2013, which was $20.87 and $15.70, respectively.
	-2	The total includes 888,174 and 963,221 performance-based options at December 31, 2014 and December 31, 2013, respectively.
	-3	Outstanding options, net of forfeiture rate
Schedule of stock option valuation assumptions	The fair value was determined by applying the Black-Scholes-Merton option pricing model, utilizing the following weighted-average assumptions:
			Year Ended
			December 31,
			2014		2013			2012
	Expected dividend yield		—	%	—	%		—	%
	Expected volatility		35.19-37.47%		35.42-40.00%			32.85-34.38
	Risk-free interest rate		1.79-2.18%		1.25-2.00%			0.92-1.04%
	Expected average life of options		6-7 years		7 years			6-7 years
Schedule of Restricted Stock Units Activity	A summary of RSU activity for the year ended December 31, 2014 is as follows:
			Unvested RSUs
	Outstanding at December 31, 2013		576,132
	Granted		188,891
	Vested		—
	Forfeited		—
	Unvested at December 31, 2014		765,023

COMMITMENTS_AND_CONTINGENCIES_

COMMITMENTS AND CONTINGENCIES - (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Schedule of future minimum operating lease payments	As of December 31, 2014, future minimum lease payments under the non-cancelable operating lease agreement are as follows:
		Lease
		Obligations
	Year ending December 31:
	2015	$	2,133
	2016	1,607
	2017	50
	2018	8
	2019	—
	Total minimum payments	$	3,798

INCOME_TAXES_Tables

INCOME TAXES - (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Summary of the loss before benefit from income taxes	The following table summarizes the loss before benefit from income taxes:
		Year Ended
		December 31,
		2014				2013				2012
	United States	$	(45,392	)		$	(37,884	)		$	(40,344	)
	Foreign	(14,359		)		(8,370		)		(5,352		)
	Total	$	(59,751	)		$	(46,254	)		$	(45,696	)
Summary of benefit from income taxes	The benefit from income taxes is as follows:
		Year Ended
		December 31,
		2014				2013				2012
	Current:
	Federal	$	—			$	—			$	—
	State	105				80				74
	Foreign	—				71				80
	Deferred:
	Federal	(16,636		)		(12,590		)		(12,396		)
	State	(975		)		(1,969		)		(1,583		)
	Foreign	(3,042		)		(1,681		)		(1,575		)
	Change in valuation allowance	20,434				7,748				2,359
	Income tax benefit	$	(114	)		$	(8,341	)		$	(13,041	)
Summary of deferred tax liabilities	The Company’s net deferred liability consists of the following:
		December 31,
		2014				2013
	Net operating loss (NOL) carryforwards	$	24,697			$	13,322
	Research and development and alternative minimum tax (AMT) credit carryforward	1,907				1,443
	Inventory	6,703				6,481
	Stock-based compensation	4,456				3,254
	Intellectual property agreements	3,227				4,303
	Other deferred temporary differences	3,717				2,989
	Intangible assets	(14,797		)		(22,534		)
	Valuation allowance	(34,952		)		(14,518		)
	Net deferred tax liability	$	(5,042	)		$	(5,260	)
Summary of reconciliation for effective tax rate	The following table summarizes a reconciliation of the U.S. statutory federal income tax rate to the Company’s effective tax rate, as a percentage of loss before income tax benefit for the years ended December 31, 2014, 2013 and 2012:
		Year Ended
		December 31,
		2014			2013			2012
	Federal tax at statutory rates	34	%		34	%		34	%
	State taxes, net of federal benefit	2.3			2.3			2.3
	Tax credits	0.6			0.5			—
	Permanent difference	1.7			0.1			0.1
	Foreign income taxes	(2.0	)		(1.8	)		(1.0	)
	Change in valuation allowance	(34.2	)		(16.8	)		(5.3	)
	Tax rate adjustment and other	(2.2	)		(0.3	)		(1.6	)
	Income tax benefit	0.2	%		18	%		28.5	%
Summary of deferred tax asset valuation allowance	The following reflects a rollforward of the deferred tax asset valuation allowance for the years ended December 31, 2014, 2013 and 2012:
		Year Ended
		December 31,
		2014				2013				2012
	Beginning	$	(14,518	)		$	(6,770	)		$	(4,411	)
	Increase to allowance	(20,434		)		(7,748		)		(2,359		)
	Decrease to allowance	—				—				—
	Ending	$	(34,952	)		$	(14,518	)		$	(6,770	)

NET_LOSS_PER_SHARE_Tables

NET LOSS PER SHARE - (Tables)	12 Months Ended
	Dec. 31, 2014
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 the Company’s common stockholders:
		Year Ended
		December 31,
		2014				2013			2012
	Net loss per common share:
	Net loss	$	(59,637	)		$	(37,913	)	$	(32,655	)
	Less: accretion and adjustment of Series A Preferred and Series B Preferred	6,879				(19,439		)	(9,954		)
	Net loss attributable to common stockholders	$	(52,758	)		$	(57,352	)	$	(42,609	)
	Basic and diluted loss per common share
	Basic and diluted weighted average common shares outstanding	31,887,246				22,238,632			21,920,512
	Basic and diluted loss per common share	$	(1.65	)		$	(2.58	)	$	(1.94	)
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	Diluted loss per share for the years ended December 31, 2014, 2013 and 2012 does not reflect the following weighted average potential common shares, as the effect would be antidilutive:
		Year Ended
		December 31,
		2014			2013			2012
	Series A Preferred and Series B Preferred	—			5,576,955			4,326,853
	Stock options	4,277,229			4,179,119			4,659,470
	Restricted stock units	765,023			576,132			—

SEGMENT_AND_GEOGRAPHICAL_CONCE1

SEGMENT AND GEOGRAPHICAL CONCENTRATION - (Tables)	12 Months Ended
	Dec. 31, 2014
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:
		Year Ended
		December 31,
		2014		2013		2012
	United States	$	133,110	$	111,772	$	99,845
	International	53,562		45,812		35,300
	Total	$	186,672	$	157,584	$	135,145
Schedule of Revenue by Products	The following table represents domestic revenue by procedure category. To further align its procedure categorizations, beginning in the second quarter of 2014, the Company began to report MIS sales attributable to complex spine procedures, which were historically reported in the minimally invasive category, within the complex spine category.  Accordingly, the complex spine category presented below includes MIS sales attributable to complex spine procedures of $5,937 and $4,905 for the years ended December 31, 2013 and 2012, respectively, which was historically reported in the minimally invasive category.
		Year Ended
		December 31,
		2014		2013		2012
	Complex spine	$	54,030	$	46,442	$	42,697
	Minimally invasive	20,670		18,403		16,766
	Degenerative	58,410		46,927		40,382
		133,110		111,772		99,845
	International	53,562		45,812		35,300
	Total	$	186,672	$	157,584	$	135,145
Schedule of Long-lived Assets by Geographic Areas	The following table represents long-lived assets (1) by geographic area:
		December 31,
		2014		2013
	United States	$	23,684	$	15,454
	International	1,928		2,795
	Total	$	25,612	$	18,249
	(1) Long-lived assets includes property and equipment and surgical instruments included in other assets.

QUARTERLY_FINANCIAL_DATA_UNAUD1

QUARTERLY FINANCIAL DATA (UNAUDITED) - (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Data	The following tables summarize the unaudited quarterly statements of operations for the Company for 2014 and 2013. The tables include all necessary adjustments, consisting only of normal recurring adjustments necessary in the opinion of management for a fair statement of the results for interim periods.
		31-Dec-14			30-Sep-14			30-Jun-14			31-Mar-14
	Revenue	$	49,309		$	47,624		$	47,488		$	42,251
	Gross profit	33,092			31,489			31,454			27,837
	Loss from operations	(8,552		)	(12,906		)	(12,813		)	(13,698		)
	Net loss	(11,067		)	(16,140		)	(17,683		)	(14,747		)
	Net loss per common share	(0.30		)	(0.43		)	(0.32		)	(0.71		)
		31-Dec-13			30-Sep-13			30-Jun-13			31-Mar-13
	Revenue	$	42,609		$	39,776		$	40,101		$	35,098
	Gross profit	27,339			27,994			27,711			24,378
	Loss from operations	(12,667		)	(9,559		)	(10,956		)	(11,739		)
	Net loss	(11,972		)	(6,178		)	(8,884		)	(10,879		)
	Net loss per common share	(0.79		)	(0.28		)	(0.43		)	(1.09		)

GENERAL_AND_SUMMARY_OF_SIGNIFI3

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Reverse Stock Split, Pro Forma Presentation, and Initial Public Offering (Details) (USD $)	0 Months Ended		12 Months Ended			1 Months Ended			2 Months Ended
In Thousands, except Share data, unless otherwise specified	13-May-14	Apr. 21, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2014	Nov. 30, 2013	Jun. 30, 2012	Jun. 30, 2013
		Rate
Class of Stock [Line Items]
Reverse stock split ratio		0.4115
Stock issued during the period (in shares)	8,825,000
Repayments of Lines of Credit	$23,500		$23,500	$2,000	$0
Repayments of Related Party Debt			39,212	0	0
Notes to Stockholders [Member]
Class of Stock [Line Items]
Repayments of Related Party Debt	40,495
Common Stock [Member]
Class of Stock [Line Items]
Stock issued during the period (in shares)						121,111	57,448	66,244	126,235
Share Price (in usd per share)						$19.05	$12.73	$9.82	$10.74
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)	2.43
Shares of common stock issued upon conversion of convertible preferred stock (in shares)	5,577,016
Series A Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Temporary Equity, Cumulative Dividends	11,932
Series B Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Temporary Equity, Cumulative Dividends	6,615
IPO [Member] | Common Stock [Member]
Class of Stock [Line Items]
Share Price (in usd per share)	$15
Proceeds from Issuance Initial Public Offering	118,862
Payments for Commissions	9,266
Payments of Stock Issuance Costs	$4,283

GENERAL_AND_SUMMARY_OF_SIGNIFI4

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Goodwill and Intangible Assets (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Significant Accounting Policies [Line Items]
Goodwill impairment loss	$0	$0	$0
Indefinite-lived intangible assets impairment loss		0	0
Finite-lived intangible assets impairment loss	$0	$0	$0
Minimum [Member]
Significant Accounting Policies [Line Items]
Finite-lived intangible assets, estimated useful lives	4 years
Maximum [Member]
Significant Accounting Policies [Line Items]
Finite-lived intangible assets, estimated useful lives	7 years

GENERAL_AND_SUMMARY_OF_SIGNIFI5

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Assets (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Significant Accounting Policies [Line Items]
Net loss	($11,067)	($16,140)	($17,683)	($14,747)	($11,972)	($6,178)	($8,884)	($10,879)	($59,637)	($37,913)	($32,655)
Net loss attributable to common stockholders									-52,758	-57,352	-42,609
Net loss per share (basic and diluted) (in dollars per share)	($0.30)	($0.43)	($0.32)	($0.71)	($0.79)	($0.28)	($0.43)	($1.09)	($1.65)	($2.58)	($1.94)
Surgical and Medical Instruments [Member]
Significant Accounting Policies [Line Items]
Long-term assets, estimated useful life									5 years
Surgical and Medical Instruments [Member] | Scenario, Previously Reported [Member]
Significant Accounting Policies [Line Items]
Long-term assets, estimated useful life									3 years
Service Life [Member]
Significant Accounting Policies [Line Items]
Cost of revenue									4,827	6,732
Net loss									4,817	5,520
Net loss attributable to common stockholders									$4,817	$5,520
Net loss per share (basic and diluted) (in dollars per share)									$0.15	$0.25

GENERAL_AND_SUMMARY_OF_SIGNIFI6

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fair Value Measurements (Details)	12 Months Ended
	Dec. 31, 2014
Minimum [Member]
Significant Accounting Policies [Line Items]
Discount rate	15.00%
Maximum [Member]
Significant Accounting Policies [Line Items]
Discount rate	17.50%

GENERAL_AND_SUMMARY_OF_SIGNIFI7

GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Shipping and Handling Costs (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Shipping and Handling Costs	$3,403	$2,311	$2,143

ACCOUNTS_RECEIVABLE_Details

ACCOUNTS RECEIVABLE - (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Receivables [Abstract]
Accounts receivable	$36,431	$35,271
Allowances	-2,494	-2,447
Accounts receivable, net	$33,937	$32,824

ACCOUNTS_RECEIVABLE_Allowances

ACCOUNTS RECEIVABLE - Allowances (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning	($2,447)	($2,217)	($2,020)
Additions	-436	-230	-383
Write-offs	389	0	186
Ending	($2,494)	($2,447)	($2,217)

INVENTORY_Details

INVENTORY - (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Inventory [Line Items]
Finished goods	$78,331	$64,539
Inventory allowances	-25,714	-25,316
Inventory, net	52,617	39,223
Surgical and Medical Instruments [Member]
Inventory [Line Items]
Inventory, net	$8,491	$5,285

PROPERTY_AND_EQUIPMENT_Details

PROPERTY AND EQUIPMENT - (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$10,708	$7,836
Less accumulated depreciation and amortization	-6,488	-4,858
Property and equipment, net	4,220	2,978
Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Property and equipment, gross	2,725	2,412
Software [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Property and equipment, gross	3,923	2,376
Computer equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Property and equipment, gross	1,445	1,265
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,109	1,098
Furniture and office equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Property and equipment, gross	1,048	673
Vehicles [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$458	$12

PROPERTY_AND_EQUIPMENT_Additio

PROPERTY AND EQUIPMENT - Additional Information (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Abstract]
Depreciation expense	$1,626	$1,505	$1,589

GOODWILL_AND_INTANGIBLE_ASSETS2

GOODWILL AND INTANGIBLE ASSETS - (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Intangible Asset by Major Class [Line Items]
Goodwill	$121,814	$121,814
Indefinite-lived intangible assets	14,078	14,696
Subject to amortization, Gross	145,714	145,213
Accumulated Amortization	-118,183	-95,453
Total	27,531	49,760
Intangible Assets, Gross	281,606	281,723
Intangible Assets, Net	163,423	186,270
Amortization expense	22,946	30,195	30,062
Developed Technology Rights [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross	62,000	61,600
Accumulated Amortization	-46,460	-36,466
Total	15,540	25,134
Licensed technology [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross	52,600	52,600
Accumulated Amortization	-52,175	-43,947
Total	425	8,653
License technology Reclassified from In-process Research and Development [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	6 years
Subject to amortization, Gross	400	0
Customer Relationships [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross	29,700	29,700
Accumulated Amortization	-18,563	-14,320
Total	11,137	15,380
Patents and other [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Subject to amortization, Gross	1,414	1,313
Accumulated Amortization	-985	-720
Total	429	593
Trademarks [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Indefinite-lived intangible assets	12,900	12,900
In-process research and development [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Indefinite-lived intangible assets	900	1,500
Impairment of Intangible Assets (Excluding Goodwill)	200
Other [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Indefinite-lived intangible assets	$278	$296
Minimum [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	4 years
Minimum [Member] | Developed Technology Rights [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	4 years	4 years
Minimum [Member] | Licensed technology [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	4 years	4 years
Minimum [Member] | Customer Relationships [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	4 years	4 years
Minimum [Member] | Patents and other [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	2 years	2 years
Maximum [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	7 years
Maximum [Member] | Developed Technology Rights [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	6 years	6 years
Maximum [Member] | Licensed technology [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	6 years	6 years
Maximum [Member] | Customer Relationships [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	7 years	7 years
Maximum [Member] | Patents and other [Member]
Schedule of Intangible Asset by Major Class [Line Items]
Estimated Useful Lives	17 years	17 years

GOODWILL_AND_INTANGIBLE_ASSETS3

GOODWILL AND INTANGIBLE ASSETS - Schedule of Expected Amortization Expense (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]
2015	$10,275
2016	10,205
2017	6,590
2018	95
2019 and thereafter	366
Total	$27,531	$49,760

OTHER_ASSETS_Details

OTHER ASSETS - (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Cash and Cash Equivalents Items [Line Items]
Surgical instruments, net	$21,392	$15,271
Restricted cash	8,114	0
Other	166	143
Total	29,672	15,414
Surgical instruments accumulated amortization	18,610	15,007
Amortization expense	6,494	2,814	5,940
Other Assets [Member] | Escrow for Tenant Improvements [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	6,667
Other Assets [Member] | Deposits on Pending Bids or Contracts with Customers [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$1,447

ACCRUED_EXPENSES_Details

ACCRUED EXPENSES - (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Payables and Accruals [Abstract]
Accrued commissions	$4,942	$2,837
Accrued royalties	2,464	2,230
Stock option awards liability	0	2,076
Other	2,671	1,617
Total	$10,077	$8,760

DEBT_Debt_Summary_Details

DEBT - Debt Summary (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Long-term and Short-term Debt [Line Items]
Bank line of credit	$0	$23,500
Notes to stockholders	0	19,650
Total debt	0	45,770
Less unamortized discounts	0	-2,620
Debt, net of discounts	0	43,150
Line of Credit [Member]
Schedule of Long-term and Short-term Debt [Line Items]
Bank line of credit	0	23,500
Notes to Stockholders [Member]
Schedule of Long-term and Short-term Debt [Line Items]
Notes to stockholders	$0	$22,270

DEBT_Bank_Line_of_Credit_Narra

DEBT - Bank Line of Credit Narrative (Details) (USD $)	0 Months Ended	12 Months Ended			0 Months Ended
	13-May-14	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 21, 2014
Debt Instrument [Line Items]
Repayments of Lines of Credit	$23,500,000	$23,500,000	$2,000,000	$0
Interest expense		2,205,000	2,810,000	1,222,000
Revolving Credit Facility [Member] | Credit Agreement 2012 [Member]
Debt Instrument [Line Items]
Repayments of Lines of Credit	23,500,000
Interest Payable	38,000
Interest expense		373,000	1,383,000	964,000
Revolving Credit Facility [Member] | Credit Agreement 2012 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Minimum unused borrowing capacity		5,000,000
Revolving Credit Facility [Member] | Credit Agreement 2012 [Member] | Silicon Valley Bank and Comerica Bank [Member]
Debt Instrument [Line Items]
Amounts available under credit agreement					40,000,000
Borrowing base calculated as a percentage of accounts receivable, percentage					85.00%
Line Of Credit Facility, Borrowing Base Calculation, Percentage Of Borrowing Base Plus Percentage Of Value Of Eligible Inventory					50.00%
Borrowing base limitation calculation , percentage of borrowing case plus percentage of value of eligible inventory, percentage of eligible inventory					35.00%
Borrowing base limitation calculation threshold, threshold percentage of borrowing rate					40.00%
Borrowing base limitation calculation threshold, threshold amount					10,000,000
Debt Instrument, covenant, minimum required quick ratio					1.2
Revolving Credit Facility [Member] | Credit Agreement 2012 [Member] | Base Rate [Member] | Silicon Valley Bank and Comerica Bank [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					0.75%
Revolving Credit Facility [Member] | Credit Agreement 2012 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Silicon Valley Bank and Comerica Bank [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					2.50%
Revolving Credit Facility [Member] | Credit Agreement 2012 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Silicon Valley Bank and Comerica Bank [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					3.75%
Revolving Credit Facility [Member] | Credit Agreement 2012 [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Amortization of issuance and discount costs included in interest expense		338,000	383,000	147,000
Minimum unused borrowing capacity		26,535,000
Revolving Credit Facility [Member] | Amended Credit Agreement 2012 [Member]
Debt Instrument [Line Items]
Minimum unused borrowing capacity					32,628,000
Revolving Credit Facility [Member] | Amended Credit Agreement 2012 [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Amounts available under credit agreement					40,000,000
Letter of Credit [Member] | Amended Credit Agreement 2012 [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Amounts available under credit agreement					10,000,000
Letters of Credit Outstanding, Amount		6,100
Revolving Credit Facility, Swing Line Loan [Member] | Amended Credit Agreement 2012 [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Amounts available under credit agreement					5,000,000
Corporate Headquarters [Member] | Letter of Credit [Member] | Amended Credit Agreement 2012 [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount		$6,000

DEBT_Notes_to_Stockholders_Det

DEBT - Notes to Stockholders (Details) (USD $)	0 Months Ended	12 Months Ended			1 Months Ended			2 Months Ended
In Thousands, except Share data, unless otherwise specified	13-May-14	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2014	Nov. 30, 2013	Jun. 30, 2012	Jun. 30, 2013
Debt Instrument [Line Items]
Stock issued during the period (in shares)	8,825,000
Sale of common stock pursuant to securities purchase agreements			$2,177	$650
Notes to stockholders		0	19,650
Payment of dividends on Series A and Series B redeemable convertible preferred stock		14,634	14,884	4,650
Related Party Discount on Prepayment of Debt	4,825	4,825	0	0
Interest expense		2,205	2,810	1,222
Accretion of preferred stock to fair value			19,439	9,954
Notes to Stockholders [Member]
Debt Instrument [Line Items]
Notes to stockholders		0	22,270
Major Stockholder [Member] | Notes to Stockholders [Member]
Debt Instrument [Line Items]
Notes to stockholders					16,942	16,970	5,300
Stated interest rate					10.00%	10.00%	10.00%
Payment of dividends on Series A and Series B redeemable convertible preferred stock					14,634	14,884	4,650
Amount outstanding of all note payable to stockholders	39,212
Accrued interest	1,283
Interest expense		1,324	1,410	275
Accretion of preferred stock to fair value		4,928	98	18
Common Stock [Member]
Debt Instrument [Line Items]
Stock issued during the period (in shares)					121,111	57,448	66,244	126,235
Share Price (in usd per share)					$19.05	$12.73	$9.82	$10.74
Sale of common stock pursuant to securities purchase agreements					$2,308	$731	$650	$1,356

PREFERRED_STOCK_Rollforward_of

PREFERRED STOCK - Rollforward of Convertible Preferred Stock (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Redeemable Convertible Preferred Stock [Roll Forward]
Accretion of preferred stock to fair value		$19,439	$9,954
Series A Redeemable Convertible Preferred Stock [Member]
Redeemable Convertible Preferred Stock [Roll Forward]
Preferred stock, Shares Authorized, Beginning (in shares)	7,300,000	7,300,000	7,300,000
Preferred Stock, Shares Outstanding, Beginning (in shares)	7,250,885	7,250,885	7,250,885
Preferred Stock, Value, Beginning	56,667	50,525	45,793
Issuance of preferred stock		0	0
Issuance costs of preferred stock			0
Payment of dividend	-11,932
Accretion of preferred stock to fair value	1,195	6,142	4,732
Adjustment of preferred stock to fair value prior to conversion	-1,170	-5,304	-7,298
Conversion to common stock, Authorized (in shares)	-7,300,000
Stock Converted During Period, Shares, Conversion of Convertible Securities	-7,250,885
Stock Converted During Period, Value, Conversion of Convertible Securities	-44,760
Preferred stock, Shares Authorized, Ending (in shares)	0	7,300,000	7,300,000
Preferred Stock, Shares Outstanding, Ending (in shares)	0	7,250,885	7,250,885
Preferred Stock, Value, Ending	0	56,667	50,525
Series B Redeemable Convertible Preferred Stock [Member]
Redeemable Convertible Preferred Stock [Roll Forward]
Preferred stock, Shares Authorized, Beginning (in shares)	6,500,000	5,249,000	5,249,000
Preferred Stock, Shares Outstanding, Beginning (in shares)	6,301,290	3,263,368	2,624,672
Preferred Stock, Value, Beginning	52,414	27,543	19,926
Issuance of preferred stock, Authorized (in shares)		1,251,000	0
Issuance of preferred stock, Outstanding (in shares)		3,037,922	638,696
Issuance of preferred stock		11,574	2,433
Issuance costs of preferred stock			-38
Payment of dividend	-6,615
Accretion of preferred stock to fair value	-15	13,297	5,222
Adjustment of preferred stock to fair value prior to conversion	-6,889
Conversion to common stock, Authorized (in shares)	-6,500,000
Stock Converted During Period, Shares, Conversion of Convertible Securities	-6,301,290
Stock Converted During Period, Value, Conversion of Convertible Securities	-38,895
Preferred stock, Shares Authorized, Ending (in shares)	0	6,500,000	5,249,000
Preferred Stock, Shares Outstanding, Ending (in shares)	0	6,301,290	3,263,368
Preferred Stock, Value, Ending	$0	$52,414	$27,543

PREFERRED_STOCK_Narrative_Deta

PREFERRED STOCK - Narrative (Details) (USD $)	12 Months Ended	0 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	13-May-14	Dec. 31, 2014	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2011
Class of Stock [Line Items]
Preferred stock issued (in shares)			0
Preferred Stock, Shares Authorized (in shares)			100,000,000
Preferred Stock, Shares Outstanding (in shares)			0
Series A Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock issued (in shares)				6,561,680
Preferred stock issued				$25,000
Preferred Stock, Dividend Rate, Percentage	10.00%
Dividends	10,564
Series B Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock issued (in shares)	3,037,922				638,696	2,624,672
Preferred stock issued	11,574				2,433	10,000
Preferred Stock, Dividend Rate, Percentage	14.00%
Dividends	5,136
Common Stock [Member]
Class of Stock [Line Items]
Shares of common stock issued upon conversion of convertible preferred stock (in shares)		5,577,016
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)		2.43
Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Payments of dividends		18,547
Conversion of Series A Redeemable Convertible Preferred Stock [Member] | Common Stock [Member]
Class of Stock [Line Items]
Shares of common stock issued upon conversion of convertible preferred stock (in shares)		2,983,902
Conversion of Series B Redeemable Convertible Preferred Stock [Member] | Common Stock [Member]
Class of Stock [Line Items]
Shares of common stock issued upon conversion of convertible preferred stock (in shares)		2,593,114
Beneficial Owner [Member] | Series A Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock issued (in shares)				689,205

STOCKBASED_COMPENSATION_Alloca

STOCK-BASED COMPENSATION - Allocation of Share-based Compensation (Details) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense		$5,807	$2,879	$2,243
Stock based compensation related to stock option liability awards	0	0	1,291
Employee Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense		5,537	2,664	2,195
Non-Employee Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense		270	215	48
Cost of Sales [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense		424	532	32
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense		439	92	136
Selling and Marketing Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense		2,146	889	696
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense		$2,798	$1,366	$1,379

STOCKBASED_COMPENSATION_Summar

STOCK-BASED COMPENSATION - Summary of Stock Option Activity (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding Beginning Balance (in shares)	4,179,119
Granted (in shares)	707,796
Exercised (in shares)	-512,933
Expired (in shares)	-31,888
Forfeited (in shares)	-64,865
Outstanding Ending Balance (in shares)	4,277,229	4,179,119
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)	$8.18
Granted, Weighted-Average Exercise Price (in usd per share)	$15.04
Exercised, Weighted-Average Exercise Price (in usd per share)	$6.10
Expired, Weighted-Average Exercise Price (in usd per share)	$4.41
Forfeited, Weighted-Average Exercise Price (in usd per share)	$10.90
Ending, Weighted-Average Exercise Price (in usd per share)	$9.55	$8.18
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, Weighted- Average Remaining Contractual Term (years)	5 years 9 months 29 days	5 years 7 months 20 days
Outstanding, Weighted- Average Remaining Contractual Term (years)	5 years 9 months 29 days	5 years 7 months 20 days
Outstanding, Aggregate Intrinsic Value	$31,434
Outstanding, Aggregate Intrinsic Value	48,418	31,434
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]
Vested or expected to vest (in shares)	4,102,613
Vested or expected to vest, Weighted-Average Exercise Price (in usd per share)	$9.51
Vested or expected to vest, Weighted-Average Remaining Contractual Term (years)	5 years 9 months 11 days
Vested or expected to vest, Aggregate Intrinsic Value	46,595
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested [Abstract]
Vested (in shares)	2,302,735
Vested, Weighted-Average Exercise Price (in usd per share)	$7.93
Vested, Weighted-Average Remaining Contractual Term (years)	4 years 5 months 8 days
Vested, Aggregate Intrinsic Value	$29,797
Fair value valuation, estimated fair market value of stock (in usd per share)	$20.87	$15.70
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding Ending Balance (in shares)	888,174	963,221

STOCKBASED_COMPENSATION_Weight

STOCK-BASED COMPENSATION - Weighted-Average Assumptions (Details) (Employee Stock Option [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
Expected average life of options		7 years
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	35.19%	35.42%	32.85%
Risk-free interest rate	1.79%	1.25%	0.92%
Expected average life of options	6 years		6 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	37.47%	40.00%	34.38%
Risk-free interest rate	2.18%	2.00%	1.04%
Expected average life of options	7 years		7 years

STOCKBASED_COMPENSATION_Summar1

STOCK-BASED COMPENSATION - Summary of Restricted Stock Unit Activity (Details) (Restricted Stock Units (RSUs) [Member])	12 Months Ended
	Dec. 31, 2014
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, Beginning Balance (in shares)	576,132
Granted (in shares)	188,891
Vested (in shares)	0
Forfeited (in shares)	0
Outstanding, Ending Balance (in shares)	765,023

STOCKBASED_COMPENSATION_Narrat

STOCK-BASED COMPENSATION - Narrative (Details) (USD $)	1 Months Ended	12 Months Ended			0 Months Ended
In Thousands, except Share data, unless otherwise specified	Feb. 28, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	7-May-14	Apr. 21, 2014
		plan				Installment
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Stock Plans		4
Number of shares available under employee stock purchase plan (in shares)		384,339
Allocated stock-based compensation expense		$5,807	$2,879	$2,243
Stock Issued during period under employee stock purchase plans (in shares)		27,184
Stock Issued During Period, Value, Employee Stock Purchase Plan		346
Fair value of employee stock options		1,386	2,034	2,376
Weighted average grand date fair value (in usd per share)		$5.54	$4.53	$4.95
Share-based compensation, forfeiture rate		3.10%		3.10%
Intrinsic value of options exercised		5,191	2,372	1,276
Share based compensation, award options to purchase	377,312
Deferred compensation, accrued liability			1,910
Allocated stock-based compensation expense from change in fair value of the liability			1,292
Vested or expected to vest (in shares)		4,102,613
Employees Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock Purchase Plan, Prerequisite for Participation, Minimum Hours Per Week of Employed					20 hours
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate					2.00%
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent					85.00%
Allocated stock-based compensation expense		80
Employees Stock [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock Purchase Plan, Common Stock Purchase, Payroll Deduction, Percentage					1.00%
Employees Stock [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock Purchase Plan, Common Stock Purchase, Payroll Deduction, Percentage					10.00%
Equity Award Plan for 2010 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		50,546
Options, vesting period (years)			4 years
Options, service term (years)			10 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Installments			2
Equity Award Plan for 2010 [Member] | Performance-based Vesting Criteria [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting percentage of the option			50.00%
Equity Award Plan for 2010 [Member] | Time-based Vesting Schedule [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting percentage of the option			50.00%
Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		753,601
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense		4,253	2,318
Unrecognized compensation expense weighted average period for recognition		2 years 29 days	2 years 6 months 14 days
Employee Stock Option [Member] | Performance-based Vesting Criteria [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense		3,224	3,453
Unrecognized compensation expense weighted average period for recognition		6 years 3 months
Employee Stock Option [Member] | Omnibus Incentive Plan [Member] | Immediately Vested [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested or expected to vest (in shares)					2,833,000
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense		3,004	0
Unrecognized compensation expense						8,993
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Installments						2
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Modification, Modified Number						576,132
Allocated Share-based Compensation Expense, Amount Per Unit						$15.61
Restricted Stock Units (RSUs) [Member] | Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated stock-based compensation expense		$616
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Installments					3
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized					188,891

DEFINED_CONTRIBUTION_PLAN_Deta

DEFINED CONTRIBUTION PLAN - (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Contributions paid to the defined contribution plan	$1,458	$1,096	$861

COMMITMENTS_AND_CONTINGENCIES_1

COMMITMENTS AND CONTINGENCIES - (Details) (USD $)	12 Months Ended			1 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Nov. 30, 2011	Dec. 11, 2014
Long-term Purchase Commitment [Line Items]
Initial payment to acquire proprietary technology	$118,000	$117,000	$250,000
Licensed technology [Member]
Long-term Purchase Commitment [Line Items]
Other commitment	1,613,000
Minimum contractual term	5 years
Licensed technology [Member] | Minimum [Member]
Long-term Purchase Commitment [Line Items]
Future maximum royalty payments	2.00%
Licensed technology [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Future maximum royalty payments	10.00%
In-process research and development [Member]
Long-term Purchase Commitment [Line Items]
Future maximum royalty payments				7.00%
Initial payment to acquire proprietary technology	100,000
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
Milestone for ending royalty payments, cumulative sales				20,000,000
In-process research and development [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Other commitment				13,350,000
Corporate Headquarters [Member]
Long-term Purchase Commitment [Line Items]
Rent payment	78,000
Yearly percentage increase to rent payment	3.00%
Corporate Headquarters [Member] | Headquarter Facilities [Member] | Virginia [Member]
Long-term Purchase Commitment [Line Items]
Rent payment					3,201,000
Yearly percentage increase to rent payment					2.50%
Area of Real Estate Property					145,819
Lease term (in years)					186 months
Lessee Leasing Arrangements, Operating Leases, Term After Completion of Building Improvements that Lease Begins					5 months
Lessee Leasing Arrangements, Operating Lease, Period of Lease Abated					6 months
Capital Lease, Security Deposit, Letter of Credit Pledged					6,000
Capital Lease, Expected Future Leasehold Improvements	6,667,000
Minimum lease payments - 2016	1,337,000
Minimum lease payments - 2017	3,282,000
Minimum lease payments - 2018	3,364,000
Minimum lease payments - 2019	3,448,000
Minimum lease payments - Thereafter	46,427,000
Manufacturing Facility [Member]
Long-term Purchase Commitment [Line Items]
Rent payment	$6,000
Yearly percentage increase to rent payment	4.00%

COMMITMENTS_AND_CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Schedule of Future Lease Payments (Details) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Lease Obligations
2015	$2,133
2016	1,607
2017	50
2018	8
2019	0
Total minimum payments	$3,798

RELATED_PARTIES_Details

RELATED PARTIES - (Details) (USD $)	0 Months Ended	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Jun. 10, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Underwriters [Member]
Related Party Transaction [Line Items]
Stock Issued During Period, Shares, Issued for Services (in shares)	1,000,000
Stock Issued During Period, Value, Issued for Services (in usd per share)	$15
Major Stockholder [Member] | Related Party Transaction, Management Service Fee [Member]
Related Party Transaction [Line Items]
General and administrative		$372	$775	$500

INCOME_TAXES_Summary_of_Loss_B

INCOME TAXES - Summary of Loss Before Benefit from Income Taxes (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
United States	($45,392)	($37,884)	($40,344)
Foreign	-14,359	-8,370	-5,352
Loss before income taxes	($59,751)	($46,254)	($45,696)

INCOME_TAXES_Benefit_from_Inco

INCOME TAXES - Benefit from Income Taxes (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current:
Federal	$0	$0	$0
State	105	80	74
Foreign	0	71	80
Deferred:
Federal	-16,636	-12,590	-12,396
State	-975	-1,969	-1,583
Foreign	-3,042	-1,681	-1,575
Change in valuation allowance	20,434	7,748	2,359
Income tax benefit	($114)	($8,341)	($13,041)

INCOME_TAXES_Schedule_of_net_d

INCOME TAXES - Schedule of net deferred liability (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Components of Deferred Tax Assets and Liabilities [Abstract]
Net operating loss (NOL) carryforwards	$24,697	$13,322
Research and development and alternative minimum tax (AMT) credit carryforward	1,907	1,443
Inventory	6,703	6,481
Stock-based compensation	4,456	3,254
Intellectual property agreements	3,227	4,303
Other deferred temporary differences	3,717	2,989
Intangible assets	-14,797	-22,534
Valuation allowance	-34,952	-14,518	-6,770	-4,411
Net deferred tax liability	($5,042)	($5,260)

INCOME_TAXES_Reconciliation_of

INCOME TAXES - Reconciliation of the U.S. statutory federal income tax rate to the Company’s effective tax rate (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal tax at statutory rates	34.00%	34.00%	34.00%
State taxes, net of federal benefit	2.30%	2.30%	2.30%
Tax credits	0.60%	0.50%	0.00%
Permanent difference	1.70%	0.10%	0.10%
Foreign income taxes	-2.00%	-1.80%	-1.00%
Change in valuation allowance	-34.20%	-16.80%	-5.30%
Tax rate adjustment and other	-2.20%	-0.30%	-1.60%
Income tax benefit	0.20%	18.00%	28.50%

INCOME_TAXES_Rollforward_of_de

INCOME TAXES - Rollforward of deferred tax asset valuation allowance (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred Tax Asset Valuation Allowance [Roll Forward]
Beginning	($14,518)	($6,770)	($4,411)
Increase to allowance	-20,434	-7,748	-2,359
Decrease to allowance	0	0	0
Ending	($34,952)	($14,518)	($6,770)

INCOME_TAXES_Narrative_Details

INCOME TAXES - Narrative (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Operating Loss Carryforwards [Line Items]
Net operating loss (NOL) carryforwards	$24,697	$13,322
Net operating carryforwards subject to expire	1,907
Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Net operating carryforwards not subject to expire	$6,045

NET_LOSS_PER_SHARE_Details

NET LOSS PER SHARE - (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net loss per common share:
Net loss	($11,067)	($16,140)	($17,683)	($14,747)	($11,972)	($6,178)	($8,884)	($10,879)	($59,637)	($37,913)	($32,655)
Less: accretion and adjustment of Series A Preferred and Series B Preferred									6,879
Less: accretion and adjustment of Series A Preferred and Series B Preferred										-19,439	-9,954
Net loss attributable to stockholders									($52,758)	($57,352)	($42,609)
Basic and diluted loss per common share
Basic and diluted (in shares)									31,887,246	22,238,632	21,920,512
Basic and diluted (in dollars per share)	($0.30)	($0.43)	($0.32)	($0.71)	($0.79)	($0.28)	($0.43)	($1.09)	($1.65)	($2.58)	($1.94)

NET_LOSS_PER_SHARE_Antidilutiv

NET LOSS PER SHARE - Antidilutive Shares (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Series A and B Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	0	5,576,955	4,326,853
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	4,277,229	4,179,119	4,659,470
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Earnings Per Share (in shares)	765,023	576,132	0

SEGMENT_AND_GEOGRAPHICAL_CONCE2

SEGMENT AND GEOGRAPHICAL CONCENTRATION - Narrative (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
									Segment
									category
Segment Reporting Information [Line Items]
Number of reportable segments									1
Number of sales categories									3
Revenue	$49,309	$47,624	$47,488	$42,251	$42,609	$39,776	$40,101	$35,098	$186,672	$157,584	$135,145
International [Member]
Segment Reporting Information [Line Items]
Revenue									53,562	45,812	35,300
United States [Member]
Segment Reporting Information [Line Items]
Revenue									133,110	111,772	99,845
United States [Member] | Complex Spine Attributable to Minimally Invasive Surgery [Member]
Segment Reporting Information [Line Items]
Revenue										5,937	4,905
Sales Revenue, Net [Member]
Segment Reporting Information [Line Items]
Revenue									186,672	157,584	135,145
Sales Revenue, Net [Member] | International [Member]
Segment Reporting Information [Line Items]
Revenue									53,562	45,812	35,300
Sales Revenue, Net [Member] | United States [Member]
Segment Reporting Information [Line Items]
Revenue									$133,110	$111,772	$99,845
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | International [Member]
Segment Reporting Information [Line Items]
International revenue as a percentage of total revenue									28.70%
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | United States [Member]
Segment Reporting Information [Line Items]
International revenue as a percentage of total revenue									10.00%

SEGMENT_AND_GEOGRAPHICAL_CONCE3

SEGMENT AND GEOGRAPHICAL CONCENTRATION - Revenues by Geographic Area (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenue	$49,309	$47,624	$47,488	$42,251	$42,609	$39,776	$40,101	$35,098	$186,672	$157,584	$135,145
United States [Member]
Segment Reporting Information [Line Items]
Revenue									133,110	111,772	99,845
International [Member]
Segment Reporting Information [Line Items]
Revenue									53,562	45,812	35,300
Sales Revenue, Net [Member]
Segment Reporting Information [Line Items]
Revenue									186,672	157,584	135,145
Sales Revenue, Net [Member] | United States [Member]
Segment Reporting Information [Line Items]
Revenue									133,110	111,772	99,845
Sales Revenue, Net [Member] | International [Member]
Segment Reporting Information [Line Items]
Revenue									$53,562	$45,812	$35,300

SEGMENT_AND_GEOGRAPHICAL_CONCE4

SEGMENT AND GEOGRAPHICAL CONCENTRATION - Revenues by Product (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue from External Customer [Line Items]
Revenue	$49,309	$47,624	$47,488	$42,251	$42,609	$39,776	$40,101	$35,098	$186,672	$157,584	$135,145
United States [Member]
Revenue from External Customer [Line Items]
Revenue									133,110	111,772	99,845
United States [Member] | Complex Spine [Member]
Revenue from External Customer [Line Items]
Revenue									54,030	46,442	42,697
United States [Member] | Minimally Invasive [Member]
Revenue from External Customer [Line Items]
Revenue									20,670	18,403	16,766
United States [Member] | Degenerative [Member]
Revenue from External Customer [Line Items]
Revenue									58,410	46,927	40,382
International [Member]
Revenue from External Customer [Line Items]
Revenue									$53,562	$45,812	$35,300

SEGMENT_AND_GEOGRAPHICAL_CONCE5

SEGMENT AND GEOGRAPHICAL CONCENTRATION - Long-Lived Assets by Geographic Area (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	$25,612	$18,249
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	23,684	15,454
International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	$1,928	$2,795

QUARTERLY_FINANCIAL_DATA_UNAUD2

QUARTERLY FINANCIAL DATA (UNAUDITED) - (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Selected Quarterly Financial Information [Abstract]
Revenue	$49,309	$47,624	$47,488	$42,251	$42,609	$39,776	$40,101	$35,098	$186,672	$157,584	$135,145
Gross profit	33,092	31,489	31,454	27,837	27,339	27,994	27,711	24,378	123,872	107,422	91,183
Loss from operations	-8,552	-12,906	-12,813	-13,698	-12,667	-9,559	-10,956	-11,739	-47,969	-44,921	-45,508
Net loss	($11,067)	($16,140)	($17,683)	($14,747)	($11,972)	($6,178)	($8,884)	($10,879)	($59,637)	($37,913)	($32,655)
Net loss per common share (in dollars per share)	($0.30)	($0.43)	($0.32)	($0.71)	($0.79)	($0.28)	($0.43)	($1.09)	($1.65)	($2.58)	($1.94)

SUBSEQUENT_EVENTS_Narrative_De

SUBSEQUENT EVENTS - Narrative (Details) (USD $)	0 Months Ended	12 Months Ended			0 Months Ended
In Thousands, except Share data, unless otherwise specified	13-May-14	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 02, 2015	Jun. 10, 2014	Feb. 12, 2015
Subsequent Event [Line Items]
Stock issued during the period (in shares)	8,825,000
Proceeds from Issuance of Common Stock		$121,898	$0	$0
Subsequent Event [Member]
Subsequent Event [Line Items]
Shares issued in follow-on offering (in shares)					6,044,990
Shares issued (in dollars per share)					$18.75
Stock issued during the period (in shares)					2,044,990
Stock issued during the period, shareholders shares (in shares)					4,000,000
Proceeds from Issuance of Common Stock					$35,900
Underwriters [Member]
Subsequent Event [Line Items]
Shares issued (in dollars per share)						$15
Stock Issued During Period, Shares, Issued for Services (in shares)						1,000,000
Underwriters [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Shares issued (in dollars per share)							$18.75
Stock Issued During Period, Shares, Issued for Services (in shares)							906,748