Credit Facilities	12 Months Ended
Dec. 31, 2015
Line of Credit Facility [Abstract]
Credit Facilities	Credit Facilities 2.25% Convertible Senior Notes On December 10, 2013, the Company issued $86.3 million aggregate principal amount of 2.25% Senior Notes. The 2.25% Senior Notes mature on December 15, 2018 unless earlier repurchased by the Company or converted. The Company received net proceeds from the sale of the 2.25% Senior Notes of approximately $82.6 million, after deducting underwriting discounts and commissions and offering expenses payable by the Company. Interest is payable on the 2.25% Senior Notes on June 15 and December 15 of each year, beginning June 15, 2014. The 2.25% Senior Notes are governed by the terms of a base indenture (the “Base Indenture”), as supplemented by the first supplemental indenture relating to the 2.25% Senior Notes (the “First Supplemental Indenture,” and together with the Base Indenture, the “2.25% Senior Notes Indenture”), between the Company and Wells Fargo Bank, National Association (the “Trustee”), each of which were entered into on December 10, 2013. The 2.25% Senior Notes are senior unsecured obligations and are: (a) senior in right of payment to the Company’s future indebtedness that is expressly subordinated in right of payment to the Notes; (b) equal in right of payment to the Company’s existing and future unsecured indebtedness that is not so subordinated; (c) effectively junior to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness; and (d) structurally junior to all existing and future indebtedness (including trade payables) incurred by the Company’s subsidiaries. The Company may not redeem the 2.25% Senior Notes prior to December 15, 2016. On or after December 15, 2016, the Company may redeem for cash all or any portion of the 2.25% Senior Notes, at its option, but only if the closing sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period ending on, and including, the second trading day immediately preceding the date on which the Company provides notice of redemption, exceeds 130% of the conversion price on each applicable trading day. The redemption price will equal 100% of the principal amount of the 2.25% Senior Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. No sinking fund is provided for the 2.25% Senior Notes. Holders may convert their 2.25% Senior Notes at any time prior to the close of business on the business day immediately preceding September 15, 2018 only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on March 31, 2014, if the closing sale price of the Company’s common stock, for at least 20 trading days (whether or not consecutive) in the period of 30 consecutive trading days ending on the last trading day of the calendar quarter immediately preceding the calendar quarter in which the conversion occurs, is more than 130% of the conversion price of the 2.25% Senior Notes in effect on each applicable trading day; (2) during the five consecutive business-day period following any five consecutive trading-day period in which the trading price for the 2.25% Senior Notes for each such trading day was less than 98% of the closing sale price of the Company’s common stock on such date multiplied by the then-current conversion rate; (3) if the Company calls all or any portion of the 2.25% Senior Notes for redemption, at any time prior to the close of business on the second scheduled trading day prior to the redemption date; or (4) upon the occurrence of specified corporate events. On or after September 15, 2018 until the close of business on the second scheduled trading day immediately preceding the stated maturity date, holders may surrender their 2.25% Senior Notes for conversion at any time, regardless of the foregoing circumstances. Upon conversion, the Company will at its election pay or deliver, as the case may be, cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock. The initial conversion rate will be 41.6051 shares of the Company’s common stock for each $1,000 principal amount of 2.25% Senior Notes, which represents an initial conversion price of approximately $24.04 per share. Following certain corporate transactions that occur on or prior to the stated maturity date or the Company’s delivery of a notice of redemption, the Company will increase the conversion rate for a holder that elects to convert its 2.25% Senior Notes in connection with such a corporate transaction. If a fundamental change (as defined in the 2.25% Senior Notes Indenture) occurs prior to the stated maturity date, holders may require the Company to purchase for cash all or any portion of their 2.25% Senior Notes at a fundamental change purchase price equal to 100% of the principal amount of the 2.25% Senior Notes to be purchased, plus accrued and unpaid interest to, but excluding, the fundamental change purchase date. The 2.25% Senior Notes Indenture contains customary terms and covenants and events of default with respect to the 2.25% Senior Notes. If an event of default (as defined in the 2.25% Senior Notes Indenture) occurs and is continuing, either the Trustee or the holders of at least 25% in aggregate principal amount of the outstanding 2.25% Senior Notes may declare the principal amount of the 2.25% Senior Notes to be due and payable immediately by notice to the Company (with a copy to the Trustee). If an event of default arising out of certain events of bankruptcy, insolvency or reorganization involving the Company or a significant subsidiary (as set forth in the 2.25% Senior Notes Indenture) occurs with respect to us, the principal amount of the 2.25% Senior Notes and accrued and unpaid interest, if any, will automatically become immediately due and payable. The Company was not required to separate the conversion option in the 2.25% Senior Notes under ASC 815, "Derivatives and Hedging", and has the ability to settle the 2.25% Senior Notes in cash, common stock or a combination of cash and common stock, at its option. In accordance with cash conversion guidance contained in ASC 470-20, "Debt with Conversion and Other Options", the Company accounted for the 2.25% Senior Notes by allocating the issuance proceeds between the liability and the equity component. The equity component is classified in stockholders’ equity and the resulting discount on the liability component is accreted such that interest expense equals the Company’s nonconvertible debt borrowing rate. The separation was performed by first determining the fair value of a similar debt that does not have an associated equity component. That amount was then deducted from the initial proceeds of the 2.25% Senior Notes as a whole to arrive at a residual amount, which was allocated to the conversion feature that is classified as equity. The initial fair value of the indebtedness was $66.9 million resulting in a $19.3 million allocation to the embedded conversion option. The embedded conversion option was recorded in stockholders’ equity and as debt discount, to be subsequently accreted to interest expense over the term of the 2.25% Senior Notes. Underwriting discounts and commissions and offering expenses totaled $3.7 million and were allocated between the liability and the equity component in proportion to the allocation of proceeds and accounted for as debt issuance costs and equity issuance costs, respectively. As a result, $2.9 million attributable to the indebtedness was recorded as deferred financing costs in other assets, to be subsequently amortized as interest expense over the term of the 2.25% Senior Notes, and $0.8 million attributable to the equity component was recorded a a reduction to additional paid-in-capital in stockholders’ equity. As of December 31, 2015, the Company had outstanding borrowings of $74.0 million, and deferred financing costs of $1.9 million, related to the 2.25% Senior Notes. There are no principal payments due during the term. Annual interest expense on these 2.25% Senior Notes will range from $5.7 million to $6.9 million through maturity. Capped Call Transactions On December 10, 2013, in connection with the pricing of the 2.25% Senior Notes and the exercise in full of their overallotment option by the underwriters, the Company entered into privately-negotiated capped call transactions (the “Capped Call Transactions”) with Bank of America, N.A., an affiliate of Merrill Lynch, Pierce, Fenner & Smith Incorporated. The Capped Call Transactions initial conversion rate and number of options substantially corresponds to each $1,000 principal amount of 2.25% Senior Notes. The Company used approximately $7.4 million of the net proceeds from the 2.25% Senior Notes offering to pay for the cost of the Capped Call Transactions. The Capped Call Transactions are separate transactions entered into by the Company with Bank of America, N.A., are not part of the terms of the 2.25% Senior Notes and will not change the holders’ rights under the 2.25% Senior Notes. The Capped Call Transactions have anti-dilution adjustments substantially similar to those applicable to the 2.25% Senior Notes. The Capped Call Transactions are derivative instruments that qualify for classification within stockholders’ equity because they meet an exemption from mark-to-market derivative accounting. The Capped Call Transactions are expected generally to reduce the potential dilution and/or offset potential cash payments that the Company is required to make in excess of the principal amount upon conversion of the 2.25% Senior Notes in the event that the market price per share of the Company’s common stock, as measured under the terms of the Capped Call Transactions, is greater than the strike price of the Capped Call Transactions, which initially corresponds to the $24.04 conversion price of the 2.25% Senior Notes. If, however, the market price per share of the Company’s common stock, as measured under the terms of the Capped Call Transactions, exceeds the initial cap price of $29.02, there would nevertheless be dilution and/or there would not be an offset of such potential cash payments, in each case, to the extent that such market price exceeds the cap price of the Capped Call Transactions. The Company will not be required to make any cash payments to Bank of America, N.A. or any of its affiliates upon the exercise of the options that are a part of the Capped Call Transactions, but will be entitled to receive from Bank of America, N.A. (or an affiliate thereof) a number of shares of the Company’s common stock and/or an amount of cash generally based on the amount by which the market price per share of the Company’s common stock, as measured under the terms of the Capped Call Transactions, is greater than the strike price of the Capped Call Transactions during the relevant valuation period under the Capped Call Transactions. However, if the market price of the Company’s common stock, as measured under the terms of the Capped Call Transactions, exceeds the cap price of the Capped Call Transactions during such valuation period under the Capped Call Transactions, the number of shares of common stock and/or the amount of cash the Company expects to receive upon exercise of the Capped Call Transactions will be capped based on the amount by which the cap price exceeds the strike price of the Capped Call Transactions. For any conversions of 2.25% Senior Notes prior to the close of business on the 55th scheduled trading day immediately preceding the stated maturity date of the 2.25% Senior Notes, including without limitation upon an acquisition of the Company or similar business combination, a corresponding portion of the Capped Call Transactions will be terminated. Upon such termination, the portion of the Capped Call Transactions being terminated will be settled at fair value (subject to certain limitations), as determined by Bank of America, N.A., in its capacity as calculation agent under the Capped Call Transactions, which the Company expects to receive from Bank of America, N.A., and no payments will be due Bank of America, N.A. The capped call expires on December 13, 2018. 3.25% Convertible Senior Notes due 2020 On November 2, 2015, the Company issued $125.0 million aggregate principal amount of 3.25% Senior Convertible Notes due 2020 (the “3.25% Senior Notes”). The 3.25% Senior Notes are governed by the Base Indenture, as amended and supplemented by the second supplemental indenture relating to the 3.25% Senior Notes (the “Second Supplemental Indenture,” and together with the Base Indenture, the “3.25% Senior Notes Indenture”), dated as of November 2, 2015, by and between the Company and the Trustee. The 3.25% Senior Notes are senior unsecured obligations and are: senior in right of payment to the Company’s future indebtedness that is expressly subordinated in right of payment to the 3.25% Senior Notes; equal in right of payment to the Company’s existing and future unsecured indebtedness that is not so subordinated, including the 2.25% Senior Notes; effectively junior to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness; and structurally junior to all existing and future indebtedness (including trade payables) incurred by the Company’s subsidiaries. The 3.25% Senior Notes accrue interest at a rate of 3.25% per year, payable semi-annually in arrears on May 1 and November 1 of each year, commencing May 1, 2016. The 3.25% Senior Notes mature on November 1, 2020, unless earlier purchased, redeemed or converted into shares of common stock in accordance with the terms of the 3.25% Senior Notes Indenture. The Company may not redeem the 3.25% Senior Notes prior to November 1, 2018. On or after November 1, 2018, the Company may redeem for cash all or any portion of the 3.25% Senior Notes, at its option, but only if the closing sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period ending on, and including, the second trading day immediately preceding the date on which the Company provides notice of redemption, exceeds 130% of the conversion price on each applicable trading day. The redemption date can be no sooner than 30 trading days from the date on which notice of redemption is provided to the holders, during which time, up until two trading days prior to the redemption, the holders may elect to convert all or a portion of the 3.25% Senior Notes into shares of the Company’s common stock. The redemption price will equal 100% of the principal amount of the 3.25% Senior Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. No sinking fund is provided for the 3.25% Senior Notes. The 3.25% Senior Notes are convertible at the option of the holders: (1) in the calendar quarter following any quarter in which, for at least 20 out of the 30 consecutive trading days (whether or not consecutive) ending on the last day of the quarter, the closing price of the Company’s common stock is more than 130% of the then-current conversion price of the 3.25% Senior Notes; (2) in the five business days following any five day period in which the trading price per $1,000 note was less than 98% of the product of the closing sale price of the Company’s common stock and the current conversion rate; (3) in the event that the Company has provided notice of redemption, but no later than two trading days prior to Company’s proposed redemption date; or (4) upon the occurrence of specified corporate events. On or after August 1, 2020 until the close of business on the second scheduled trading day immediately preceding the stated maturity date, holders may surrender their 3.25% Senior Notes for conversion at any time, regardless of the foregoing circumstances. The initial conversion rate of the 3.25% Senior Notes is 89.4314 shares of the Company’s common stock per $1,000 principal amount of the 3.25% Senior Notes, which is equivalent to an initial conversion price of approximately $11.18 per share. The conversion rate is subject to adjustment upon the occurrence of certain specified events. Upon conversion, the Company will at its election pay or deliver, as the case may be, cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock. If a fundamental change (as defined in the 3.25% Senior Notes Indenture) occurs prior to the stated maturity date, holders may require the Company to purchase for cash all or any portion of their 3.25% Senior Notes at a fundamental change purchase price equal to 100% of the principal amount of the 3.25% Senior Notes to be purchased, plus accrued and unpaid interest. The 3.25% Senior Notes Indenture contains customary terms and covenants and events of default with respect to the 3.25% Senior Notes. If an event of default (as defined in the 3.25% Senior Notes Indenture) occurs and is continuing, either the Trustee or the holders of at least 25% in aggregate principal amount of the outstanding 3.25% Senior Notes may declare the principal amount of the 3.25% Senior Notes to be due and payable immediately by notice to the Company (with a copy to the Trustee). If an event of default arising out of certain events of bankruptcy, insolvency or reorganization involving the Company or a significant subsidiary (as set forth in the 3.25% Senior Notes Indenture) occurs with respect to us, the principal amount of the 3.25% Senior Notes and accrued and unpaid interest, if any, will automatically become immediately due and payable. Upon issuance and through December 31, 2015, the Company was not required to separate the conversion option from the 3.25% Senior Notes under ASC 815, "Derivatives and Hedging". However, because the Company has the ability to settle the 3.25% Senior Notes in cash, common stock or a combination of cash and common stock, the Company applied the cash conversion guidance contained in ASC 470-20, "Debt With Conversion and other Options", and accounted for the 3.25% Senior Notes by allocating the issuance proceeds between the liability-classified debt component and a separate equity component attributable to the conversion option. The equity component is classified in stockholders’ equity and the resulting discount on the liability component is accreted such that interest expense equals the Company’s borrowing rate for nonconvertible loan products of similar duration. The separation was performed by first determining the fair value of a similar debt that does not have an associated equity component. That amount was then deducted from the initial proceeds of the 3.25% Senior Notes as a whole to arrive at a residual amount, which was allocated to the conversion feature that is classified as equity. The initial fair value of the indebtedness was $97.8 million resulting in a $27.2 million allocation to the embedded conversion option. The embedded conversion option was recorded in stockholders’ equity and as a debt discount, to be subsequently accreted to interest expense over the term of the 3.25% Senior Notes. Underwriting discounts and commissions and offering expenses totaled $3.7 million and were allocated between the liability and the equity component in proportion to the allocation of proceeds and accounted for as debt issuance costs and equity issuance costs, respectively. As a result, $2.9 million attributable to the indebtedness was recorded as deferred financing costs in other assets, to be subsequently amortized as interest expense over the term of the 3.25% Senior Notes, and $0.8 million attributable to the equity component was recorded as a reduction to additional paid-in-capital in stockholders’ equity. In connection with the acquisition of TriVascular in February 2016, the Company issued 13.6 million shares of common stock as consideration to the sellers of TriVascular. As a result of such consideration, the quantity of authorized common shares available for future issuance was reduced to a level insufficient to honor all of the potential common shares underlying instruments then outstanding. Such instruments include the conversion options related to the 3.25% Senior Notes and 2.25% Senior Notes, employee stock options, restricted stock units, and shares reserved for issuance under the Company’s employee stock purchase plan. The Company is currently evaluating whether or not the creation of this authorized share deficiency in February 2016 will, on a prospective basis, require the Company to separate as a stand-alone derivative the portion of the conversion option for which no authorized shares are available to effect share settlement in the event of a conversion. The Company expects to authorize an amount of common shares sufficient to resolve the deficiency during the second quarter of 2016. As of December 31, 2015, the Company had outstanding borrowings of $98.5 million, and deferred financing costs of $2.8 million, related to the 3.25% Senior Notes. There are no principal payments due during the term. Annual interest expense on these 3.25% Senior Notes will range from $9.1 million to $10.7 million through maturity. Wells Fargo line of credit In October 2009, the Company entered into a revolving credit facility with Wells Fargo Bank (“Wells”), which was last amended on February 3, 2015, whereby the Company may borrow up to $20 million, subject to the calculation and limitation of a borrowing base (the “Wells Credit Facility”). A sub-feature in the line of credit allowed for the issuance of up to $7.5 million million in letters of credit. The Wells Credit Facility was collateralized by all of the Company's assets, except its intellectual property. The Wells Credit Facility contained financial covenants requiring the Company to maintain certain credit ratios, limit pre-tax net loss, limit capital expenditures and operating lease expenses in any calendar year. The financial covenants as of and for the three and twelve months ended December 31, 2015 were no longer applicable due to the termination of the Wells Credit Facility on July 21, 2015. The Wells Credit Facility also contains a “material adverse change” clause (“MAC”). If the Company encounters difficulties that would qualify as a MAC in its (i) operations, (ii) condition (financial or otherwise), or (iii) ability to repay amounts outstanding under the Wells Credit Facility, it could be canceled at Wells' sole discretion. Wells could then elect to declare the indebtedness, together with accrued interest and other fees, to be immediately due and payable and proceed against any collateral securing such indebtedness. On July 21, 2015, the Company terminated the credit facility. As of the termination date, the Company had no outstanding borrowings or letters of credits issued under the Wells Credit Facility. Bank of America line of credit On July 21, 2015, the Company entered into a revolving credit facility with Bank of America, N.A. (“BOA”), whereby the Company may borrow up to $20.0 million (the “BOA Credit Facility”). All amounts owing under the BOA Credit Facility will become due and payable upon its expiration on July 21, 2017. A sub-feature in the line of credit allows for the issuance of up to $10.0 million in letters of credit. As of December 31, 2015, the Company had no letters of credit issued under the BOA credit facility. The BOA Credit Facility is collateralized by all of the Company's assets, except its intellectual property. The BOA Credit Facility can be terminated at any time during the two years by Company upon three business day notice. The BOA Credit Facility usage is priced at a spread over the one, two, three and six month LIBOR rates, and is subject to a covenant related to timely providing of publicly reported information, other indebtedness and a liquidity covenant tied to “Unencumbered Liquid Assets” ("ULA") (as defined here) of not less than $30.0 million. ULA means the following assets (excluding assets of any retirement plan): (a) cash and cash equivalents; (b) marketable securities invested in accordance with the Company’s investment policy and (c) marketable securities invested in accordance with any update to the Company’s investment policy so long as such update has been approved by BOA in its reasonable discretion. Such assets must be (i) held in the United States at BOA and/or its affiliates, (ii) not the subject of any lien, pledge, security interest or other arrangement with any creditor (other than BOA or one of BOA’s affiliates) to have his claim satisfied out of the asset (or proceeds thereof) prior to the general creditors of the owner of the asset, (iii) held solely in the name of one or more credit parties subject to this covenant (with no other persons or entities having ownership rights therein), (iv) convertible to cash within five (5) days, and (v) not counted or included to satisfy any other liquidity requirement under any other obligation, whether with BOA or any other lender, unless otherwise expressly agreed by BOA in writing. The Company was in compliance with this covenant as of December 31, 2015. If not in default, the Company has the ability to reduce the ULA covenant requirement by reducing the BOA Credit Facility, with the ULA maintained at 1.5 times the BOA Credit Facility. As of December 31, 2015, the Company had no borrowings under the BOA Credit Facility.

Credit Facilities

2.25% Convertible Senior Notes

On December 10, 2013, the Company issued $86.3 million aggregate principal amount of 2.25% Senior Notes. The 2.25% Senior Notes mature on December 15, 2018 unless earlier repurchased by the Company or converted. The Company received net proceeds from the sale of the 2.25% Senior Notes of approximately $82.6 million, after deducting underwriting discounts and commissions and offering expenses payable by the Company. Interest is payable on the 2.25% Senior Notes on June 15 and December 15 of each year, beginning June 15, 2014.

The 2.25% Senior Notes are governed by the terms of a base indenture (the “Base Indenture”), as supplemented by the first supplemental indenture relating to the 2.25% Senior Notes (the “First Supplemental Indenture,” and together with the Base Indenture, the “2.25% Senior Notes Indenture”), between the Company and Wells Fargo Bank, National Association (the “Trustee”), each of which were entered into on December 10, 2013.

The 2.25% Senior Notes are senior unsecured obligations and are: (a) senior in right of payment to the Company’s future indebtedness that is expressly subordinated in right of payment to the Notes; (b) equal in right of payment to the Company’s existing and future unsecured indebtedness that is not so subordinated; (c) effectively junior to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness; and (d) structurally junior to all existing and future indebtedness (including trade payables) incurred by the Company’s subsidiaries.

The Company may not redeem the 2.25% Senior Notes prior to December 15, 2016. On or after December 15, 2016, the Company may redeem for cash all or any portion of the 2.25% Senior Notes, at its option, but only if the closing sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period ending on, and including, the second trading day immediately preceding the date on which the Company provides notice of redemption, exceeds 130% of the conversion price on each applicable trading day. The redemption price will equal 100% of the principal amount of the 2.25% Senior Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. No sinking fund is provided for the 2.25% Senior Notes.

Holders may convert their 2.25% Senior Notes at any time prior to the close of business on the business day immediately preceding September 15, 2018 only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on March 31, 2014, if the closing sale price of the Company’s common stock, for at least 20 trading days (whether or not consecutive) in the period of 30 consecutive trading days ending on the last trading day of the calendar quarter immediately preceding the calendar quarter in which the conversion occurs, is more than 130% of the conversion price of the 2.25% Senior Notes in effect on each applicable trading day; (2) during the five consecutive business-day period following any five consecutive trading-day period in which the trading price for the 2.25% Senior Notes for each such trading day was less than 98% of the closing sale price of the Company’s common stock on such date multiplied by the then-current conversion rate; (3) if the Company calls all or any portion of the 2.25% Senior Notes for redemption, at any time prior to the close of business on the second scheduled trading day prior to the redemption date; or (4) upon the occurrence of specified corporate events. On or after September 15, 2018 until the close of business on the second scheduled trading day immediately preceding the stated maturity date, holders may surrender their 2.25% Senior Notes for conversion at any time, regardless of the foregoing circumstances.

Upon conversion, the Company will at its election pay or deliver, as the case may be, cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock.

The initial conversion rate will be 41.6051 shares of the Company’s common stock for each $1,000 principal amount of 2.25% Senior Notes, which represents an initial conversion price of approximately $24.04 per share. Following certain corporate transactions that occur on or prior to the stated maturity date or the Company’s delivery of a notice of redemption, the Company will increase the conversion rate for a holder that elects to convert its 2.25% Senior Notes in connection with such a corporate transaction.

If a fundamental change (as defined in the 2.25% Senior Notes Indenture) occurs prior to the stated maturity date, holders may require the Company to purchase for cash all or any portion of their 2.25% Senior Notes at a fundamental change purchase price equal to 100% of the principal amount of the 2.25% Senior Notes to be purchased, plus accrued and unpaid interest to, but excluding, the fundamental change purchase date.

The 2.25% Senior Notes Indenture contains customary terms and covenants and events of default with respect to the 2.25% Senior Notes. If an event of default (as defined in the 2.25% Senior Notes Indenture) occurs and is continuing, either the Trustee or the holders of at least 25% in aggregate principal amount of the outstanding 2.25% Senior Notes may declare the principal amount of the 2.25% Senior Notes to be due and payable immediately by notice to the Company (with a copy to the Trustee). If an event of default arising out of certain events of bankruptcy, insolvency or reorganization involving the Company or a significant subsidiary (as set forth in the 2.25% Senior Notes Indenture) occurs with respect to us, the principal amount of the 2.25% Senior Notes and accrued and unpaid interest, if any, will automatically become immediately due and payable.

The Company was not required to separate the conversion option in the 2.25% Senior Notes under ASC 815, "Derivatives and Hedging", and has the ability to settle the 2.25% Senior Notes in cash, common stock or a combination of cash and common stock, at its option. In accordance with cash conversion guidance contained in ASC 470-20, "Debt with Conversion and Other Options", the Company accounted for the 2.25% Senior Notes by allocating the issuance proceeds between the liability and the equity component. The equity component is classified in stockholders’ equity and the resulting discount on the liability component is accreted such that interest expense equals the Company’s nonconvertible debt borrowing rate. The separation was performed by first determining the fair value of a similar debt that does not have an associated equity component. That amount was then deducted from the initial proceeds of the 2.25% Senior Notes as a whole to arrive at a residual amount, which was allocated to the conversion feature that is classified as equity. The initial fair value of the indebtedness was $66.9 million resulting in a $19.3 million allocation to the embedded conversion option. The embedded conversion option was recorded in stockholders’ equity and as debt discount, to be subsequently accreted to interest expense over the term of the 2.25% Senior Notes. Underwriting discounts and commissions and offering expenses totaled $3.7 million and were allocated between the liability and the equity component in proportion to the allocation of proceeds and accounted for as debt issuance costs and equity issuance costs, respectively. As a result, $2.9 million attributable to the indebtedness was recorded as deferred financing costs in other assets, to be subsequently amortized as interest expense over the term of the 2.25% Senior Notes, and $0.8 million attributable to the equity component was recorded a a reduction to additional paid-in-capital in stockholders’ equity.

As of December 31, 2015, the Company had outstanding borrowings of $74.0 million, and deferred financing costs of $1.9 million, related to the 2.25% Senior Notes. There are no principal payments due during the term. Annual interest expense on these 2.25% Senior Notes will range from $5.7 million to $6.9 million through maturity.

Capped Call Transactions

On December 10, 2013, in connection with the pricing of the 2.25% Senior Notes and the exercise in full of their overallotment option by the underwriters, the Company entered into privately-negotiated capped call transactions (the “Capped Call Transactions”) with Bank of America, N.A., an affiliate of Merrill Lynch, Pierce, Fenner & Smith Incorporated. The Capped Call Transactions initial conversion rate and number of options substantially corresponds to each $1,000 principal amount of 2.25% Senior Notes. The Company used approximately $7.4 million of the net proceeds from the 2.25% Senior Notes offering to pay for the cost of the Capped Call Transactions.

The Capped Call Transactions are separate transactions entered into by the Company with Bank of America, N.A., are not part of the terms of the 2.25% Senior Notes and will not change the holders’ rights under the 2.25% Senior Notes. The Capped Call Transactions have anti-dilution adjustments substantially similar to those applicable to the 2.25% Senior Notes. The Capped Call Transactions are derivative instruments that qualify for classification within stockholders’ equity because they meet an exemption from mark-to-market derivative accounting.

The Capped Call Transactions are expected generally to reduce the potential dilution and/or offset potential cash payments that the Company is required to make in excess of the principal amount upon conversion of the 2.25% Senior Notes in the event that the market price per share of the Company’s common stock, as measured under the terms of the Capped Call Transactions, is greater than the strike price of the Capped Call Transactions, which initially corresponds to the $24.04 conversion price of the 2.25% Senior Notes. If, however, the market price per share of the Company’s common stock, as measured under the terms of the Capped Call Transactions, exceeds the initial cap price of $29.02, there would nevertheless be dilution and/or there would not be an offset of such potential cash payments, in each case, to the extent that such market price exceeds the cap price of the Capped Call Transactions.

The Company will not be required to make any cash payments to Bank of America, N.A. or any of its affiliates upon the exercise of the options that are a part of the Capped Call Transactions, but will be entitled to receive from Bank of America, N.A. (or an affiliate thereof) a number of shares of the Company’s common stock and/or an amount of cash generally based on the amount by which the market price per share of the Company’s common stock, as measured under the terms of the Capped Call Transactions, is greater than the strike price of the Capped Call Transactions during the relevant valuation period under the Capped Call Transactions. However, if the market price of the Company’s common stock, as measured under the terms of the Capped Call Transactions, exceeds the cap price of the Capped Call Transactions during such valuation period under the Capped Call Transactions, the number of shares of common stock and/or the amount of cash the Company expects to receive upon exercise of the Capped Call Transactions will be capped based on the amount by which the cap price exceeds the strike price of the Capped Call Transactions.

For any conversions of 2.25% Senior Notes prior to the close of business on the 55th scheduled trading day immediately preceding the stated maturity date of the 2.25% Senior Notes, including without limitation upon an acquisition of the Company or similar business combination, a corresponding portion of the Capped Call Transactions will be terminated. Upon such termination, the portion of the Capped Call Transactions being terminated will be settled at fair value (subject to certain limitations), as determined by Bank of America, N.A., in its capacity as calculation agent under the Capped Call Transactions, which the Company expects to receive from Bank of America, N.A., and no payments will be due Bank of America, N.A. The capped call expires on December 13, 2018.

3.25% Convertible Senior Notes due 2020

On November 2, 2015, the Company issued $125.0 million aggregate principal amount of 3.25% Senior Convertible Notes due 2020 (the “3.25% Senior Notes”). The 3.25% Senior Notes are governed by the Base Indenture, as amended and supplemented by the second supplemental indenture relating to the 3.25% Senior Notes (the “Second Supplemental Indenture,” and together with the Base Indenture, the “3.25% Senior Notes Indenture”), dated as of November 2, 2015, by and between the Company and the Trustee.

The 3.25% Senior Notes are senior unsecured obligations and are: senior in right of payment to the Company’s future indebtedness that is expressly subordinated in right of payment to the 3.25% Senior Notes; equal in right of payment to the Company’s existing and future unsecured indebtedness that is not so subordinated, including the 2.25% Senior Notes; effectively junior to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness; and structurally junior to all existing and future indebtedness (including trade payables) incurred by the Company’s subsidiaries.

The 3.25% Senior Notes accrue interest at a rate of 3.25% per year, payable semi-annually in arrears on May 1 and November 1 of each year, commencing May 1, 2016. The 3.25% Senior Notes mature on November 1, 2020, unless earlier purchased, redeemed or converted into shares of common stock in accordance with the terms of the 3.25% Senior Notes Indenture.

The Company may not redeem the 3.25% Senior Notes prior to November 1, 2018. On or after November 1, 2018, the Company may redeem for cash all or any portion of the 3.25% Senior Notes, at its option, but only if the closing sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period ending on, and including, the second trading day immediately preceding the date on which the Company provides notice of redemption, exceeds 130% of the conversion price on each applicable trading day. The redemption date can be no sooner than 30 trading days from the date on which notice of redemption is provided to the holders, during which time, up until two trading days prior to the redemption, the holders may elect to convert all or a portion of the 3.25% Senior Notes into shares of the Company’s common stock. The redemption price will equal 100% of the principal amount of the 3.25% Senior Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. No sinking fund is provided for the 3.25% Senior Notes.

The 3.25% Senior Notes are convertible at the option of the holders: (1) in the calendar quarter following any quarter in which, for at least 20 out of the 30 consecutive trading days (whether or not consecutive) ending on the last day of the quarter, the closing price of the Company’s common stock is more than 130% of the then-current conversion price of the 3.25% Senior Notes; (2) in the five business days following any five day period in which the trading price per $1,000 note was less than 98% of the product of the closing sale price of the Company’s common stock and the current conversion rate; (3) in the event that the Company has provided notice of redemption, but no later than two trading days prior to Company’s proposed redemption date; or (4) upon the occurrence of specified corporate events. On or after August 1, 2020 until the close of business on the second scheduled trading day immediately preceding the stated maturity date, holders may surrender their 3.25% Senior Notes for conversion at any time, regardless of the foregoing circumstances.

The initial conversion rate of the 3.25% Senior Notes is 89.4314 shares of the Company’s common stock per $1,000 principal amount of the 3.25% Senior Notes, which is equivalent to an initial conversion price of approximately $11.18 per share. The conversion rate is subject to adjustment upon the occurrence of certain specified events. Upon conversion, the Company will at its election pay or deliver, as the case may be, cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock.

If a fundamental change (as defined in the 3.25% Senior Notes Indenture) occurs prior to the stated maturity date, holders may require the Company to purchase for cash all or any portion of their 3.25% Senior Notes at a fundamental change purchase price equal to 100% of the principal amount of the 3.25% Senior Notes to be purchased, plus accrued and unpaid interest.

The 3.25% Senior Notes Indenture contains customary terms and covenants and events of default with respect to the 3.25% Senior Notes. If an event of default (as defined in the 3.25% Senior Notes Indenture) occurs and is continuing, either the Trustee or the holders of at least 25% in aggregate principal amount of the outstanding 3.25% Senior Notes may declare the principal amount of the 3.25% Senior Notes to be due and payable immediately by notice to the Company (with a copy to the Trustee). If an event of default arising out of certain events of bankruptcy, insolvency or reorganization involving the Company or a significant subsidiary (as set forth in the 3.25% Senior Notes Indenture) occurs with respect to us, the principal amount of the 3.25% Senior Notes and accrued and unpaid interest, if any, will automatically become immediately due and payable.

Upon issuance and through December 31, 2015, the Company was not required to separate the conversion option from the 3.25% Senior Notes under ASC 815, "Derivatives and Hedging". However, because the Company has the ability to settle the 3.25% Senior Notes in cash, common stock or a combination of cash and common stock, the Company applied the cash conversion guidance contained in ASC 470-20, "Debt With Conversion and other Options", and accounted for the 3.25% Senior Notes by allocating the issuance proceeds between the liability-classified debt component and a separate equity component attributable to the conversion option. The equity component is classified in stockholders’ equity and the resulting discount on the liability component is accreted such that interest expense equals the Company’s borrowing rate for nonconvertible loan products of similar duration. The separation was performed by first determining the fair value of a similar debt that does not have an associated equity component. That amount was then deducted from the initial proceeds of the 3.25% Senior Notes as a whole to arrive at a residual amount, which was allocated to the conversion feature that is classified as equity. The initial fair value of the indebtedness was $97.8 million resulting in a $27.2 million allocation to the embedded conversion option. The embedded conversion option was recorded in stockholders’ equity and as a debt discount, to be subsequently accreted to interest expense over the term of the 3.25% Senior Notes. Underwriting discounts and commissions and offering expenses totaled $3.7 million and were allocated between the liability and the equity component in proportion to the allocation of proceeds and accounted for as debt issuance costs and equity issuance costs, respectively. As a result, $2.9 million attributable to the indebtedness was recorded as deferred financing costs in other assets, to be subsequently amortized as interest expense over the term of the 3.25% Senior Notes, and $0.8 million attributable to the equity component was recorded as a reduction to additional paid-in-capital in stockholders’ equity.

In connection with the acquisition of TriVascular in February 2016, the Company issued 13.6 million shares of common stock as consideration to the sellers of TriVascular. As a result of such consideration, the quantity of authorized common shares available for future issuance was reduced to a level insufficient to honor all of the potential common shares underlying instruments then outstanding. Such instruments include the conversion options related to the 3.25% Senior Notes and 2.25% Senior Notes, employee stock options, restricted stock units, and shares reserved for issuance under the Company’s employee stock purchase plan. The Company is currently evaluating whether or not the creation of this authorized share deficiency in February 2016 will, on a prospective basis, require the Company to separate as a stand-alone derivative the portion of the conversion option for which no authorized shares are available to effect share settlement in the event of a conversion. The Company expects to authorize an amount of common shares sufficient to resolve the deficiency during the second quarter of 2016.

As of December 31, 2015, the Company had outstanding borrowings of $98.5 million, and deferred financing costs of $2.8 million, related to the 3.25% Senior Notes. There are no principal payments due during the term. Annual interest expense on these 3.25% Senior Notes will range from $9.1 million to $10.7 million through maturity.

Wells Fargo line of credit

In October 2009, the Company entered into a revolving credit facility with Wells Fargo Bank (“Wells”), which was last amended on February 3, 2015, whereby the Company may borrow up to $20 million, subject to the calculation and limitation of a borrowing base (the “Wells Credit Facility”). A sub-feature in the line of credit allowed for the issuance of up to $7.5 million million in letters of credit. The Wells Credit Facility was collateralized by all of the Company's assets, except its intellectual property.

The Wells Credit Facility contained financial covenants requiring the Company to maintain certain credit ratios, limit pre-tax net loss, limit capital expenditures and operating lease expenses in any calendar year. The financial covenants as of and for the three and twelve months ended December 31, 2015 were no longer applicable due to the termination of the Wells Credit Facility on July 21, 2015.

The Wells Credit Facility also contains a “material adverse change” clause (“MAC”). If the Company encounters difficulties that would qualify as a MAC in its (i) operations, (ii) condition (financial or otherwise), or (iii) ability to repay amounts outstanding under the Wells Credit Facility, it could be canceled at Wells' sole discretion. Wells could then elect to declare the indebtedness, together with accrued interest and other fees, to be immediately due and payable and proceed against any collateral securing such indebtedness. On July 21, 2015, the Company terminated the credit facility. As of the termination date, the Company had no outstanding borrowings or letters of credits issued under the Wells Credit Facility.

Bank of America line of credit

On July 21, 2015, the Company entered into a revolving credit facility with Bank of America, N.A. (“BOA”), whereby the Company may borrow up to $20.0 million (the “BOA Credit Facility”). All amounts owing under the BOA Credit Facility will become due and payable upon its expiration on July 21, 2017. A sub-feature in the line of credit allows for the issuance of up to $10.0 million in letters of credit. As of December 31, 2015, the Company had no letters of credit issued under the BOA credit facility. The BOA Credit Facility is collateralized by all of the Company's assets, except its intellectual property. The BOA Credit Facility can be terminated at any time during the two years by Company upon three business day notice. The BOA Credit Facility usage is priced at a spread over the one, two, three and six month LIBOR rates, and is subject to a covenant related to timely providing of publicly reported information, other indebtedness and a liquidity covenant tied to “Unencumbered Liquid Assets” ("ULA") (as defined here) of not less than $30.0 million. ULA means the following assets (excluding assets of any retirement plan): (a) cash and cash equivalents; (b) marketable securities invested in accordance with the Company’s investment policy and (c) marketable securities invested in accordance with any update to the Company’s investment policy so long as such update has been approved by BOA in its reasonable discretion. Such assets must be (i) held in the United States at BOA and/or its affiliates, (ii) not the subject of any lien, pledge, security interest or other arrangement with any creditor (other than BOA or one of BOA’s affiliates) to have his claim satisfied out of the asset (or proceeds thereof) prior to the general creditors of the owner of the asset, (iii) held solely in the name of one or more credit parties subject to this covenant (with no other persons or entities having ownership rights therein), (iv) convertible to cash within five (5) days, and (v) not counted or included to satisfy any other liquidity requirement under any other obligation, whether with BOA or any other lender, unless otherwise expressly agreed by BOA in writing. The Company was in compliance with this covenant as of December 31, 2015.

If not in default, the Company has the ability to reduce the ULA covenant requirement by reducing the BOA Credit Facility, with the ULA maintained at 1.5 times the BOA Credit Facility. As of December 31, 2015, the Company had no borrowings under the BOA Credit Facility.