7. Indebtedness

At December 31, 2014 and 2013, our indebtedness was as follows:


	As of December 31,
	2014		2013
Senior Notes, due 2014 at 7.875%	$	—	$	300,000
Senior Notes, due 2015 at 5.125%		—		280,000
Senior Notes, due 2016 at 6.3%		275,000		275,000
Senior Notes, due 2017 at 5.625%		300,000		300,000
Senior Notes, due 2018 at 6.7%		350,000		350,000
Senior Notes, due 2022 at 5.0%		500,000		500,000
Senior Notes, due 2023 at 4.5%		300,000		300,000
Senior Notes, due 2024 at 4.65%		350,000		—
Senior Notes, due 2025 at 4.5%		350,000		—
Convertible Senior Notes, due 2027 at 3.8%		8,478		8,478
Unamortized discounts		(12,865)		(9,473)
Total unsecured senior notes		2,420,613		2,304,005
Unsecured revolving credit facility		18,000		—
Unsecured term loan		400,000		400,000
	$	2,838,613	$	2,704,005

Our principal debt obligations at December 31, 2014 were: (1) our $18,000 of outstanding borrowings under our $750,000 unsecured revolving credit facility; (2) our $400,000 unsecured term loan; (3) an aggregate principal amount of $2,425,000 of public issuances of unsecured senior notes; and (4) our public issuance of $8,478 outstanding principal amount of convertible senior notes.

On January 8, 2014, we amended the agreements governing our unsecured revolving credit facility and unsecured term loan with Wells Fargo Bank, National Association, as administrative agent, and a syndicate of other lenders.

As a result of the amendment, the stated maturity date of our $750,000 revolving credit facility was extended from September 7, 2015 to July 15, 2018. Subject to the payment of an extension fee and meeting certain other conditions, we have an option to further extend the stated maturity date by an additional one year to July 15, 2019. The amended credit agreement provides that we can borrow, repay and reborrow funds available under the revolving credit facility until maturity, and no principal repayment is due until maturity. The amended credit agreement includes a feature under which maximum borrowings under the revolving credit facility and term loan may be increased to up to $2,300,000 on a combined basis in certain circumstances.

Under the amendment, the interest rate payable on borrowings under the revolving credit facility was reduced from LIBOR plus a premium of 130 basis points to LIBOR plus a premium of 110 basis points, and the facility fee was reduced from 30 basis points to 20 basis points per annum on the total amount of lending commitments. Both the interest rate premium and the facility fee are subject to adjustment based upon changes to our credit ratings. As of December 31, 2014, we had $18,000 outstanding and $732,000 available under our revolving credit facility. We had $58,000 outstanding under our revolving credit facility as of February 26, 2015. As of December 31, 2014, the interest rate for the amount outstanding under our revolving credit facility was 1.27%. The weighted average interest rate for borrowings under our revolving credit facility was 1.25%, 1.50% and 1.56% for the years ended December 31, 2014, 2013 and 2012, respectively.

As a result of the amendment, the stated maturity date of our $400,000 unsecured term loan was extended from March 13, 2017 to April 15, 2019. Our term loan is prepayable without penalty at any time. Under the amendment, the interest rate payable on borrowings under the term loan agreement was reduced from LIBOR plus a premium of 145 basis points to LIBOR plus a premium of 120 basis points. The interest rate premium is subject to adjustment based on changes to our credit ratings. As of December 31, 2014, the interest rate for the amount outstanding under our term loan was 1.36%. The weighted average interest rate for borrowings under our term loan was 1.36% and 1.64% for the years ended December 31, 2014 and 2013, respectively and 1.70% for the period from March 12, 2012 (the date we entered into the term loan agreement) to December 31, 2012.

As a result of the amendments to our revolving credit facility and term loan, we recorded a $214 loss on early extinguishment of debt during the first quarter of 2014.

Our borrowings under the revolving credit facility and term loan are unsecured. The amended credit agreement provides that, with certain exceptions, a subsidiary of ours is required to guaranty our obligations under the revolving credit facility and term loan only if that subsidiary has separately incurred debt (other than nonrecourse debt), within the meaning specified in the amended credit agreement, or provided a guarantee of debt incurred by us or any of our other subsidiaries.

Our revolving credit facility and term loan agreement provides for acceleration of payment of all amounts outstanding upon the occurrence and continuation of certain events of default, such as a change of control of us, which includes RMR ceasing to act as our business manager. Our revolving credit facility and term loan agreement contains a number of covenants that restrict our ability to incur debt in excess of calculated amounts, restrict our ability to make distributions under certain circumstances and generally require us to maintain certain financial ratios. We believe we were in compliance with the terms and conditions of the agreement governing our revolving credit facility and term loan at December 31, 2014.

At December 31, 2014, we had $8,478 of our 3.8% convertible senior notes due 2027 outstanding. Our convertible senior notes are convertible if certain conditions are met (including certain changes in control) into cash equal to the principal amount of the notes and, to the extent the market price of our common shares exceeds the initial exchange price of $50.50 per share, subject to adjustment, either cash or our common shares at our option with a value based on such excess amount. Holders of our convertible senior notes may require us to repurchase all or a portion of the notes on March 15, 2017, and March 15, 2022, or upon the occurrence of certain change in control events.

On February 15, 2014, we redeemed at par all of our outstanding 7.875% senior notes due 2014 for $300,000 plus accrued and unpaid interest (an aggregate of $311,813). As a result of the redemption, we recorded a loss on extinguishment of debt of $512 during the first quarter of 2014, which represented the unamortized discount and issuance costs of these notes.

On March 12, 2014, we issued $350,000 of 4.65% unsecured senior notes due 2024 in a public offering for net proceeds of $345,949 after underwriting discounts and other offering expenses.

On August 15, 2014, we redeemed at par all of our outstanding 5⅛% senior notes due 2015 for $280,000 plus accrued and unpaid interest (an aggregate of $287,175). As a result of the redemption, we recorded a loss on extinguishment of debt of $129 during the third quarter of 2014 which represented the unamortized discount and issuance costs of these notes.

On September 12, 2014, we issued $350,000 of 4.50% unsecured senior notes due 2025 in a public offering for net proceeds of $342,786 after underwriting discounts and other offering expenses.

All of our senior notes are prepayable at any time prior to their maturity date at par plus accrued interest plus a premium equal to a make whole amount, as defined, generally designed to preserve a stated yield to the noteholder. Interest on all of our senior notes is payable semi‑annually in arrears.

The required principal payments due during the next five years and thereafter under all our outstanding debt at December 31, 2014 are as follows:


2015	$	—
2016		275,000
2017		300,000
2018		368,000
2019		400,000
Thereafter		1,508,478	(1)
	$	2,851,478

(1)

Includes our $8,478 convertible senior notes due 2027. Holders of our convertible senior notes may require us to repurchase all or a portion of the notes on March 15, 2017 and March 15, 2022, or upon the occurrence of certain change in control events.