Debt and Credit Facility

Senior Notes

In May 2012, we issued $225.0 million principal amount of 8.25% unsecured senior notes due June 1, 2020 ("Senior Notes") at 100% of the principal amount. Interest expense, including amortization of deferred financing costs, relating to the Senior Notes was $4.8 million for each of the quarters ended March 31, 2015 and March 31, 2014. A portion of the interest relating to the Senior Notes was capitalized as construction in progress. See Note 3 of Notes to Consolidated Financial Statements included in our Annual Report on Form 10-K for the year ended December 31, 2014 for additional information regarding the Senior Notes.

Cash Convertible Senior Notes

Convertible Notes. In March 2010, we issued $175.0 million principal amount of 4.50% unsecured Cash Convertible Senior Notes due April 1, 2015 ("Convertible Notes"). The Convertible Notes are not convertible into our common stock or any other securities, but instead are settled in cash. We account for the cash conversion feature of the Convertible Notes as a separate derivative instrument ("Bifurcated Conversion Feature") with the fair value on the issuance date equaling the original issuance discount for purposes of accounting for the debt component of the Convertible Notes. The following tables provide additional information regarding the Convertible Notes (in millions of dollars):



	March 31, 2015		December 31, 2014
Principal amount	$	175.0	$	175.0
Less: unamortized issuance discount	—		(2.5		)
Carrying amount, net of discount	$	175.0	$	172.5



	Quarter Ended March 31,
	2015		2014
Contractual coupon interest	$	2.0	$	2.0
Amortization of discount	2.4		2.1
Amortization of deferred financing costs	0.3		0.3
Total interest expense¹	$	4.7	$	4.4

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¹	A portion of the interest relating to the Convertible Notes was capitalized as construction in progress.

An immaterial amount of Convertible Notes was converted during 2014 pursuant to a provision that permitted early conversion. Of the remaining Convertible Notes, all but five were presented for conversion during the quarter ended March 31, 2015. The conversion value of 154.261% of par was determined over the final settlement period of 50 consecutive trading days that ended on March 27, 2015, resulting in a total payment amount to settle the Convertible Notes on April 1, 2015 of $273.8 million, comprised of a final coupon payment of $3.9 million, principal of $175.0 million and conversion premium of $94.9 million.

Convertible Note Hedge Transactions. In connection with the issuance of our Convertible Notes, we entered into privately negotiated transactions whereby we purchased cash-settled call options ("Option Assets") relating to shares of our common stock. In March 2015, we gave notice of exercise to the counterparties of the Option Assets. The aggregate payment amount that was due on April 1, 2015 to us from the counterparties to settle the Option Assets was $94.9 million, which equaled the conversion premium or the aggregate amount of cash that we paid to the holders of the converted Convertible Notes, less the principal amount thereof and interest payable thereon. As the cash received to settle the Option Assets equaled the cash we paid for the conversion premium, the net cash outflow to settle our Convertible Notes and Option Assets on April 1, 2015 was $178.9 million.

Contemporaneous with the issuance of the Convertible Notes and our purchase of the Option Assets in 2010, we sold net-share-settled warrants ("Warrants") relating to approximately 3.7 million notional shares of our common stock. The Warrants will settle ratably over a 120 trading day period beginning on July 1, 2015. As of March 31, 2015, after reflecting cumulative anti-dilution adjustments for payment of quarterly dividends paid in excess of $0.24 per share, the exercise price of the Warrants was $60.57 per share.

See Note 3 of Notes to Consolidated Financial Statements included in our Annual Report on Form 10-K for the year ended December 31, 2014 for additional information regarding the Convertible Notes, Bifurcated Conversion Feature, Option Assets and Warrants.

See "Fair Values of Financial Assets and Liabilities - All Other Financial Assets and Liabilities" in Note 9 for information relating to the estimated fair value of the Senior Notes, Convertible Notes, Bifurcated Conversion Feature and Option Assets.

Revolving Credit Facility

Our credit agreement with JPMorgan Chase Bank, N.A., as administrative agent, and the other financial institutions party thereto ("Revolving Credit Facility") provides us with a $300.0 million funding commitment through September 30, 2016. We had $281.7 million of borrowing availability under the Revolving Credit Facility at March 31, 2015, based on the borrowing base determination then in effect. At March 31, 2015, there were no borrowings under the Revolving Credit Facility and $7.6 million was being used to support outstanding letters of credit, leaving $274.1 million of net borrowing availability. The interest rate applicable to any overnight borrowings under the Revolving Credit Facility would have been 4.0% at March 31, 2015.

See Note 3 of Notes to Consolidated Financial Statements included in our Annual Report on Form 10-K for the year ended December 31, 2014 for additional information regarding the Revolving Credit Facility.