9. Debt

Convertible Notes Due 2016

In October 2011, we issued $250.0 million in aggregate principal value 1.0 percent Convertible Senior Notes due September 15, 2016 (2016 Convertible Notes). The 2016 Convertible Notes are unsecured, unsubordinated debt obligations that rank equally with all of our other unsecured and unsubordinated indebtedness. We pay interest semi-annually on March 15th and September 15th of each year. The initial conversion price is $47.69 per share and the number of underlying shares used to determine the aggregate consideration upon conversion is approximately 5.2 million shares.

Conversion can occur: (1) any time after June 15, 2016; (2) during any calendar quarter that follows a calendar quarter in which the price of our common stock exceeds 130 percent of the conversion price for at least 20 days during the 30 consecutive trading-day period ending on the last trading day of the quarter; (3) during the ten consecutive trading-day period following any five consecutive trading-day period in which the trading price of the 2016 Convertible Notes is less than 95 percent of the closing price of our common stock multiplied by the then current number of shares underlying the 2016 Convertible Notes; (4) upon specified distributions to our shareholders; (5) in connection with certain corporate transactions; or (6) in the event that our common stock ceases to be listed on the NASDAQ Global Select Market, the NASDAQ Global Market, or the New York Stock Exchange, or any of their respective successors.

The closing price of our common stock exceeded 130 percent of the conversion price of the 2016 Convertible Notes for more than 20 trading days during the 30 consecutive trading day period ended June 30, 2013. Consequently, the 2016 Convertible Notes are convertible at the election of their holders. As this conversion right is outside of our control, the 2016 Convertible Notes have been classified as a current liability on our consolidated balance sheet at June 30, 2013. This contingent conversion measurement is calculated at the end of each quarterly reporting period. Therefore, the convertibility and classification of our 2016 Convertible Notes may be subject to change depending on the price of our common stock.

At June 30, 2013, the aggregate conversion value of the 2016 Convertible Notes exceeded their par value by $95.0 million using a conversion price of $65.82, the closing price of our common stock on June 30, 2013.

Upon conversion, holders of our 2016 Convertible Notes are entitled to receive: (1) cash equal to the lesser of the par value of the notes or the conversion value (the number of shares underlying the 2016 Convertible Notes multiplied by the then current conversion price per share); and (2) to the extent the conversion value exceeds the par value of the notes, shares of our common stock. In the event of a change in control, as defined in the indenture under which the 2016 Convertible Notes have been issued, holders can require us to purchase all or a portion of their 2016 Convertible Notes for 100 percent of the notes’ par value plus any accrued and unpaid interest.

The terms of the 2016 Convertible Notes provide for settlement wholly or partially in cash. Consequently, we are required to account for their liability and equity components separately so that the subsequent recognition of interest expense reflects our non-convertible borrowing rate. Accordingly, we estimated the fair value of the 2016 Convertible Notes without consideration of the conversion option as of the date of issuance (Liability Component). The excess of the proceeds received over the estimated fair value of the Liability Component totaling $57.9 million has been recorded as the conversion option (Equity Component) and a corresponding offset has been recognized as a discount to the 2016 Convertible Notes to reduce their net carrying value. We are amortizing the discount over the five-year period ending September 15, 2016 (the expected life of the Liability Component) using the interest method and an effective rate of interest of 6.7 percent, which corresponded to our estimated non-convertible borrowing rate at the date of issuance.

Interest expense incurred in connection with our convertible notes consisted of the following (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2013		2012		2013		2012
Contractual coupon rate of interest	$	625	$	625	$	1,250	$	1,250
Discount amortization	2,786		2,611		5,499		5,164
Interest expense—convertible notes	$	3,411	$	3,236	$	6,749	$	6,414

Components comprising the carrying value of the 2016 Convertible Notes include the following (in thousands):

	June 30, 2013			December 31, 2012
Principal balance	$	250,000		$	250,000
Discount, net of accumulated amortization of $18,104 and $12,605	(39,834		)	(45,333		)
Carrying amount	$	210,166		$	204,667

Convertible Note Hedge and Warrant Transactions

In connection with the issuance of our 2016 Convertible Notes, we entered into separate convertible note hedge and warrant transactions with Deutsche Bank AG London (DB London) to reduce the potential dilutive impact upon the conversion of our convertible notes. Pursuant to the convertible note hedge, we purchased call options to acquire up to approximately 5.2 million shares of our common stock with a strike price of $47.69. The call options become exercisable upon conversion of the 2016 Convertible Notes, and will terminate upon the maturity of the 2016 Convertible Notes or the first day the 2016 Convertible Notes are no longer outstanding, whichever occurs first. We also sold DB London warrants to acquire up to approximately 5.2 million shares of our common stock with a strike price of $67.56. The warrants will expire incrementally on a series of expiration dates subsequent to the maturity date of our 2016 Convertible Notes. Both the convertible note hedge and warrant transactions will be settled on a net-share basis. If the conversion price of our 2016 Convertible Notes remains between the strike prices of the call options and warrants, our shareholders will not experience any dilution in connection with the conversion of our 2016 Convertible Notes; however, to the extent that the price of our common stock exceeds the strike price of the warrants on any or all of the series of related incremental expiration dates, we will be required to issue shares of our common stock to DB London.

Mortgage Financing

In December 2010, we entered into a Credit Agreement with Wells Fargo Bank N.A. (Wells Fargo) and Bank of America, N.A., pursuant to which we obtained $70.0 million in debt financing. The Credit Agreement matures in December 2014 and is secured by certain of our facilities in Research Triangle Park, North Carolina and Silver Spring, Maryland. Annual principal payments are based on a twenty-five year amortization schedule using a fixed rate of interest of 7.0 percent and the outstanding debt bears a floating rate of interest per annum based on the one-month LIBOR, plus a credit spread of 3.75 percent, or approximately 3.9 percent as of June 30, 2013. Alternatively, we have the option to change the rate of interest charged on the loan to 2.75 percent plus the greater of: (1) Wells Fargo’s prime rate, or (2) the federal funds effective rate plus 0.05 percent, or (3) LIBOR plus 1.0 percent. We can prepay the loan balance without being subject to a prepayment premium or penalty. The Credit Agreement subjects us to various financial and negative covenants. As of June 30, 2013, we were in compliance with these covenants.

Interest Expense

Details of interest expense presented on our consolidated statements of operations are as follows (in thousands):

	Three Months Ended June 30,					Six Months Ended June 30,
	2013		2012			2013		2012
Interest expense	$	4,520	$	4,361		$	8,956	$	8,670
Less: interest capitalized	—		(482		)	—		(905		)
Total interest expense	$	4,520	$	3,879		$	8,956	$	7,765

Temporary Equity

Temporary equity includes securities: (1) with redemption features that are outside our control; (2) that are not classified as an asset or liability; (3) that are excluded from stockholders’ equity; and (4) are not mandatorily redeemable. Amounts included in temporary equity relate to securities that are redeemable at a fixed or determinable price.

Components comprising the carrying value of temporary equity include the following (in thousands):

	June 30, 2013		December 31, 2012
Reclassification of Equity Component (1)	$	39,834	$	—
Common stock subject to repurchase (2)	10,882		10,882
Total	$	50,716	$	10,882

(1) Represents the reclassification of the Equity Component equal to the unamortized discount of our 2016 Convertible Notes as of June 30, 2013 from additional paid-in capital to temporary equity. As of June 30, 2013, our 2016 Convertible Notes were convertible at the election of their holders.

(2) In connection with our amended 2007 agreement with Toray Industries Inc. (Toray), we issued 400,000 shares of our common stock and provided Toray the right to request that we repurchase the shares at a price of $27.21.