Debt

Total debt at September 30, 2018 and December 31, 2017 consisted of the following:



	Interest rate	September 30, 2018		December 31, 2017
Notes due March 2018	5.60%	$	—	$	250,000
Notes due March 2019	6.25%	—		300,000
Notes due September 2020	3.875%	300,000		300,000
Notes due October 2021	3.625%	600,000		600,000
Notes due May 2022	4.375%	400,000		400,000
Notes due April 2023	4.7%	400,000		400,000
Notes due March 2024	4.625%	500,000		500,000
Notes due January 2037	5.25%	35,841		35,841
Notes due March 2043	6.7%	425,000		425,000
Term loans	Variable	635,000		650,000
Other debt		5,336		5,476
Principal amount		3,301,177		3,866,317
Less: unamortized costs, net		31,560		35,982
Total debt		3,269,617		3,830,335
Less: current portion long-term debt		192,649		271,057
Long-term debt		$	3,076,968	$	3,559,278

The interest rate on certain notes and term loans are subject to adjustment based on changes in our credit ratings. In the second quarter, Standard & Poor's lowered our corporate credit rating from BBB- to BB+. As a result, the interest rate on the May 2022 notes, September 2020 notes and term loans increased 0.25% and the interest rate on the October 2021 notes and the April 2023 notes will increase 0.25% effective after the next interest payment date.

On August 2, 2018, we redeemed the $300 million 6.25% notes due March 2019 and recorded an $8 million loss on the extinguishment of debt. We also repaid the $250 million of 5.6% notes that matured in March 2018 and $15 million of principal on our term loans.

Pursuant to an extension option, the maturity of our $150 million term loan was extended to August 2019.