At March 31, 2020 and September 30, 2019, outstanding standby letters of credit totaled $22.4 million and $22.8 million, respectively, under our revolving credit facilities. As of March 31, 2020 and September 30, 2019, we had $1,327.6 million and $1,327.2 million, respectively, available under our revolving credit facility.
2014 Senior Notes
On October 6, 2014, we completed a private placement offering of $800,000,000 aggregate principal amount of the unsecured 5.750% Senior Notes due 2022 (2022 Notes) and $800,000,000 aggregate principal amount of the unsecured 5.875% Senior Notes due 2024 (the 2024 Notes and, together with the 2022 Notes, the 2014 Senior Notes). On November 2, 2015, we completed an exchange offer to exchange the unregistered 2014 Senior Notes for registered notes, as well as all related guarantees. On March 16, 2018, we redeemed all of the 2022 Notes at a redemption price that was 104.313% of the principal amount outstanding plus accrued and unpaid interest. The March 16, 2018 redemption resulted in a $34.5 million prepayment premium, which was included in interest expense.
As of March 31, 2020, the estimated fair value of the 2024 Notes was approximately $736.0 million. The fair value of the 2024 Notes as of March 31, 2020 was derived by taking the mid-point of the trading prices from an observable market input (Level 2) in the secondary bond market and multiplying it by the outstanding balance of the 2024 Notes.
At any time prior to July 15, 2024, we may redeem on one or more occasions all or part of the 2024 Notes at a redemption price equal to the sum of (i) 100% of the principal amount thereof, plus (ii) a “make-whole” premium as of the date of the redemption, plus any accrued and unpaid interest to the date of redemption. In addition, on or after July 15, 2024, the 2024 Notes may be redeemed at a redemption price of 100% of the principal amount thereof, plus accrued and unpaid interest to the date of redemption.
The indenture pursuant to which the 2024 Notes were issued contains customary events of default, including, among other things, payment default, exchange default, failure to provide notices thereunder and provisions related to bankruptcy events. The indenture also contains customary negative covenants.
We were in compliance with the covenants relating to the 2024 Notes as of March 31, 2020.
2017 Senior Notes
On February 21, 2017, we completed a private placement offering of $1,000,000,000 aggregate principal amount of our unsecured 5.125% Senior Notes due 2027 (the 2017 Senior Notes) and used the proceeds to immediately retire the remaining $127.6 million outstanding on the then existing term loan B facility as well as repay $600 million of the term loan A facility and $250 million of the revolving credit facility under our Credit Agreement. On June 30, 2017, we completed an exchange offer to exchange the unregistered 2017 Senior Notes for registered notes, as well as related guarantees.
As of March 31, 2020, the estimated fair value of the 2017 Senior Notes was approximately $875.0 million. The fair value of the 2017 Senior Notes as of March 31, 2020 was derived by taking the mid-point of the trading prices from an observable market input (Level 2) in the secondary bond market and multiplying it by the outstanding balance of the 2017 Senior Notes. Interest will be payable on the 2017 Senior Notes at a rate of 5.125% per annum. Interest on the 2017 Senior Notes is payable semi-annually on March 15 and September 15 of each year, commencing on September 15, 2017. The 2017 Senior Notes will mature on March 15, 2027.
At any time and from time to time prior to December 15, 2026, we may redeem all or part of the 2017 Senior Notes, at a redemption price equal to 100% of their principal amount, plus a “make whole” premium as of the redemption date, and accrued and unpaid interest to the redemption date.
In addition, at any time and from time to time prior to March 15, 2020, we may redeem up to 35% of the original aggregate principal amount of the 2017 Senior Notes with the proceeds of one or more qualified equity