Note 12—Convertible Senior Notes

Convertible senior notes consist of the following (in thousands):

	December 31,
	2014		2015
4.25% Convertible senior notes (due 2018)	$	100,000	$	100,000
4.875% Convertible senior notes (due 2020)		115,000		115,000
	$	215,000	$	215,000

In November 2009, the Company sold an aggregate of $100.0 million principal amount of the 2014 Notes. The 2014 Notes, which were senior unsecured obligations of the Company, paid cash interest semi-annually at a rate of 4.50% per annum and matured on November 1, 2014. In July 2013, the Company repurchased an aggregate of $61.0 million principal amount of these notes at par plus accrued interest with a portion of the net proceeds from the issuance of $100.0 million principal amount of 4.25% convertible senior notes due 2018 resulting in a gain on extinguishment of $0.1 million. The remainder of these notes were redeemed at par at maturity on November 1, 2014.

ASC 470-20, “Debt with Conversion and Other Options,” requires the issuer of certain convertible debt instruments that may be settled in cash (or other assets) upon conversion to separately account for the liability (debt) and equity (conversion option) components of the instrument in a manner that reflects the issuer's non-convertible debt borrowing rate. In accordance with ASC 470-20, the Company allocated $13.7 million of the $100.0 million principal amount of the 2014 Notes to the equity component, which represents a discount to the debt that was being amortized to interest expense through November 1, 2014. Interest expense associated with the amortization of the discount was $2.0 million, $0.9 million, and nil for December 31, 2013, 2014 and 2015. The Company repurchased $61.0 million of the 2014 Notes during the year ended December 31, 2013 as discussed below, with $2.8 million of the price allocated to the repurchase of the related equity component. In addition, approximately $2.2 million of the unamortized debt discount and $0.6 million of debt issuance costs were written off in connection with the repurchase of the 2014 Notes. The remaining aggregate $39.0 million of principal amount of the 2014 Notes were redeemed at par at maturity on November 1, 2014. The balance of the discount was nil at December 31, 2014 and December 31, 2015.

In July 2013, the Company sold an aggregate of $100.0 million principal amount of the 2018 Notes. The 2018 Notes are senior unsecured obligations of the Company paying interest semi-annually in arrears on August 1 and February 1 of each year at a rate of 4.25% per annum and will mature on August 1, 2018. The initial conversion rate for the 2018 Notes will be 114.3674 shares of the Company’s common per $1,000 principal amount of notes, equivalent to an initial conversion price of approximately $8.74 per share of common stock, subject to adjustment in certain events. Holders of the 2018 Notes may convert their notes upon the occurrence of specified events. Upon conversion, the 2018 Notes will be settled in shares of the Company’s common stock. The Company used $61.0 million of the approximate $96.0 million in net proceeds from the offering to repurchase at par $61.0 million principal amount of the 2014 Notes. The remainder of the net proceeds will be used for general corporate purposes.

In June 2014, the Company sold an aggregate of $115.0 million principal amount of 4.875% Convertible Senior Notes due 2020 (the “2020 Notes”). The 2020 Notes are senior unsecured obligations of the Company paying interest semi-annually in arrears on June 1 and December 1 of each year at a rate of 4.875% per annum and will mature on June 1, 2020. The initial conversion rate for the 2020 Notes will be 103.7613 shares of our common per $1,000 principal amount of notes, equivalent to an initial conversion price of approximately $9.64 per share of common stock, subject to adjustment in certain events. Holders of the 2020 Notes may convert their notes upon the occurrence of specified events. Upon conversion, the 2020 Notes will be settled in shares of the Company’s common stock. The Company received net proceeds of approximately $110.4 million from the offering of which $24.0 million was used to repurchase 3.1 million shares of the Company’s common stock under a prepaid forward purchase contract and $39.0 million was used to redeem at par the remaining outstanding principal amount of the 2014 Notes at maturity on November 1, 2014. The remainder of the net proceeds will be used for general corporate purposes. In January 2016 the Company repurchased $2.0 million of the 2020 Notes.

Key components of the 4.50% convertible senior notes due 2014 consist of the following (in thousands):

	Years Ended December 31,
	2013		2014		2015
Contractual interest expense on the coupon	$	3,356	$	1,463	$	―
Amortization of debt discount and debt issuance costs recognized as interest expense		2,030		1,140		―
	$	5,386	$	2,603	$	―

Key components of the 4.25% convertible senior notes due 2018 consist of the following (in thousands):

	December 31,
	2014		2015
Principal amount of notes	$	100,000	$	100,000
Net carrying amount of the 2018 convertible notes	$	100,000	$	100,000

	Years Ended December 31,
	2013		2014		2015
Contractual interest expense	$	1,771	$	4,250	$	4,250
Amortization of debt issuance costs recognized as interest expense		421		835		836
	$	2,192	$	5,085	$	5,086

Key components of the 4.875% convertible senior notes due 2020 consist of the following (in thousands):

	December 31,
	2014		2015
Principal amount of notes	$	115,000	$	115,000
Net carrying amount of the 2020 convertible notes	$	115,000	$	115,000

	Years Ended December 31,
	2013		2014		2015
Contractual interest expense	$	—	$	3,135	$	5,606
Amortization of debt issuance costs recognized as interest expense		—		473		811
	$	—	$	3,608	$	6,417