Debt

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



	Interest rate	June 30, 2018		December 31, 2017
Notes due March 2018	5.60%	$	—	$	250,000
Notes due March 2019	6.25%	300,000		300,000
Notes due September 2020	3.625%	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	640,000		650,000
Other debt		5,378		5,476
Principal amount		3,606,219		3,866,317
Less: unamortized costs, net		33,410		35,982
Total debt		3,572,809		3,830,335
Less: current portion long-term debt		334,999		271,057
Long-term debt		$	3,237,810	$	3,559,278

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

During the year, we repaid the $250 million of 5.6% Notes that matured in March 2018 and $10 million of principal on our term loans.

On August 2, 2018, we redeemed the $300 million 6.25% Notes due March 2019.