Long-term debt consisted of the following at December 31, 2018 and December 31, 2019 (in thousands):

	2018			2019
Revolving credit facility	$	180,000		$	—
Senior notes		250,000			250,000
Debt issuance costs		(836	)		(647	)
Long-term debt	$	429,164		$	249,353

In November 2017, the Company entered into an amended and restated Credit Agreement. The Company incurred approximately $2.0 million of costs in connection with this amendment. Under the agreement, the Company’s revolving credit facility was increased from $500 million to $550 million and the term of the agreement was extended through November 2022. The borrowings under the Credit Agreement bear interest, at the Company’s option, at either the Base Rate (as defined in the Credit Agreement), plus an applicable margin, or LIBOR plus an applicable margin. The applicable margin for Base Rate loans is a range of 0.125% to 1.00% and the applicable margin for LIBOR loans is a range of 1.125% to 2.00%, both based on the leverage ratio of the Company at the end of each fiscal quarter. The rates at December 31, 2018 and December 31, 2019 were 4.253% and 3.02%, respectively. Borrowings under this Credit Agreement are guaranteed by certain of the Company’s operating subsidiaries. Letters of credit commitments outstanding under this agreement aggregated approximately $49.8 million and $43.7 million at December 31, 2018 and December 31, 2019, respectively, which reduced borrowing limits available to the Company.

On July 1, 2014, the Company finalized a private placement whereby the Company raised an aggregate amount of $250.0 million in debt repayable as follows (in thousands):

Tranche	Debt Amount		Maturity Date	Interest Rate
Senior Note, Series A	$	50,000	July 15, 2021		4.44	%
Senior Note, Series B		100,000	July 15, 2024		4.98	%
Senior Note, Series C		60,000	July 15, 2026		5.13	%
Senior Note, Series D		40,000	July 15, 2029		5.38	%

The Company incurred approximately $1.1 million of debt issuance costs in connection with the private placement. On August 10, 2018, the Company finalized an amended and restated intercreditor agreement related to this private placement to more closely align certain covenants and definitions with the terms under the 2017 amended and restated Credit Agreement and incurred approximately $0.5 million of additional issuance costs. These costs are presented as a direct deduction from the debt on the face of the balance sheet. Interest expense related to the Senior Notes approximated $12.4 million for the years ended December 29, 2017, December 31, 2018 and December 31, 2019. The amortization of debt issuance costs and interest expense are recorded in “Interest expense” on the consolidated statements of income. The Company made interest payments related to the Senior Notes of approximately $12.4 million during the periods ended December 29, 2017, December 31, 2018 and December 31, 2019. Interest payable of approximately $5.7 million is recorded in “Accrued expenses and other current liabilities” on the consolidated balance sheets at December 31, 2018 and December 31, 2019, respectively, related to the Senior Notes.

The Credit Agreement and private placement includes various covenants, including restrictions on indebtedness, liens, acquisitions, investments or dispositions, payment of dividends and maintenance of certain financial ratios and conditions. The Company was in compliance with these covenants at December 31, 2018 and December 31, 2019.

During the year ended December 31, 2019, the Company’s term loan of $150 million was paid off.

The Company also has in place several secondary bank credit lines for issuing letters of credit, principally for foreign contracts, to support performance and completion guarantees. Letters of credit commitments outstanding under these bank lines aggregated approximately $223.0 million and $197.3 million at December 31, 2018 and December 31, 2019, respectively.

Using a discounted cash flow technique that incorporates a market interest yield curve with adjustments for duration, optionality, and risk profile, the Company has determined that the fair value (Level 2; see “Note 19—Fair Value of Financial Instruments” below) of its debt approximates the carrying value.

Amortization of debt issuance costs for all of the Company’s debt and credit facilities for the years ended December 29, 2017, December 31, 2018 and December 31, 2019 was $0.5 million, $0.7 million and $1.0 million, respectively.