Note 3. Long-Term Debt

Long-term debt consisted of the following:



(In thousands)	March 31, 2018		December 31, 2017
Senior notes	$	45,000	$	95,000
Revolving credit facility	—		—
Total long-term debt	45,000		95,000
Less: Current maturities	—		(50,000		)
Total maturities due after one year	$	45,000	$	45,000

We had one unsecured senior note agreement with an amount outstanding of $45.0 million and $95.0 million at March 31, 2018 and December 31, 2017, respectively. Our unsecured senior note agreement calls for a scheduled principal payment of $50.0 million, which was paid on January 3, 2018, and a scheduled principal payment of $45.0 million, which is due on January 3, 2021. Interest rates on the January 3, 2018 and January 3, 2021 scheduled principal payments were 4.00% and 4.79%, respectively. The effective average interest rate on our outstanding senior note agreement was 4.79% and 4.37% at March 31, 2018 and December 31, 2017, respectively.

On December 15, 2015, we entered into an amended and restated credit agreement with Wells Fargo Bank, National Association ("Wells Fargo") serving as administrative agent for the lenders (the "Credit Agreement"). The Credit Agreement originally provided for a five-year, $250.0 million senior unsecured revolving line of credit and a $100.0 million accordion feature, which if fully exercised and approved, would expand the total borrowing capacity up to an aggregate of $350.0 million.

On September 9, 2016, we exercised a portion of the accordion feature and entered into an amendment to the Credit Agreement to increase the aggregate commitments from existing lenders by $50.0 million to an aggregate of $300.0 million. Of the $300.0 million line of credit commitments under the Credit Agreement, as amended, up to $100.0 million may be used for letters of credit and $30.0 million may be used for borrowings under the Wells Fargo Sweep Plus Loan Program (the "Sweep Program"). We utilize the Sweep Program to manage our daily cash needs, as it automatically initiates borrowings to cover overnight cash requirements primarily for working capital needs.

At our option, borrowings under the Credit Agreement bear interest at either: (i) LIBOR plus an applicable margin (based on our ratio of net debt-to-total capitalization) that ranges from 1.0% to 1.50%; or (ii) a Base Rate plus an applicable margin (based on our ratio of net debt-to-total capitalization) that ranges from 0.0% to 0.5%. Loans under the Sweep Program bear interest at the LIBOR plus applicable margin rate. Letter of credit fees equal to the applicable margin for LIBOR loans are charged quarterly in arrears on the daily average aggregate stated amount of all letters of credit outstanding during the quarter. Commitment fees ranging from 0.125% to 0.2% (based upon the ratio of net debt-to-total capitalization) are charged quarterly in arrears on the aggregate unutilized portion of the Credit Agreement. Wells Fargo, as administrative agent, also receives an annual fee for providing administrative services.

For periods covered under the Credit Agreement, the applicable margin on LIBOR loans and letter of credit fees were 1.0% and commitment fees were 0.125%. There were $68.2 million and $71.4 million of outstanding letters of credit at March 31, 2018 and December 31, 2017, respectively.