(3) Long‑term Debt

Long‑term debt consisted of the following as of December 31, 2018 and 2017 (in thousands):


	December 31,		December 31,
	2018		2017
Notes payable to banks, due in semi-annual installments, variable interest based on LIBOR, or with an interest rate of 4.00% through 2019, secured by aircraft	$	6,429	$	34,905
Notes payable to a financing company, due in semi-annual installments, variable interest based on LIBOR, or with an interest rate of 3.25% through 2021, secured by aircraft		36,324		97,612
Notes payable to banks, due in semi-annual installments plus interest at 6.10% to 6.51% through 2021, secured by aircraft		41,592		63,090
Notes payable to banks, due in monthly installments plus interest of 2.68% to 6.86% through 2025, secured by aircraft		371,300		372,157
Notes payable to banks, due in monthly installments, plus interest at 4.07% to 6.05% through 2029, secured by aircraft		105,069		49,001
Notes payable to banks, due in quarterly installments, plus interest at 3.39% to 5.08% through 2030, secured by aircraft		2,621,416		2,085,822
Notes payable to banks due in monthly installments, interest at 3.30% through 2019, secured by spare engines		3,308		9,763
Long-term debt	$	3,185,438	$	2,712,350
Current portion of long-term debt		(354,072)		(313,243)
Less long-term portion of unamortized debt issue cost, net		(21,598)		(21,761)
Long-term debt, net of current maturities and debt issue costs	$	2,809,768	$	2,377,346

Current portion of long-term debt		354,072		313,243
Less current portion of unamortized debt issue cost, net		(3,866)		(3,565)
Current portion of long-term debt, net of debt issue costs	$	350,206	$	309,678

During the year ended December 31, 2018, the Company acquired 39 new E175 aircraft. Approximately 85% of the aircraft purchase price was financed through the issuance of debt and 15% of the aircraft purchase price was paid with cash.

As of December 31, 2018 and 2017, the Company had $3.2 billion and $2.7 billion, respectively, of long‑term debt obligations primarily related to the acquisition of aircraft and certain spare engines. The average effective interest rate on the debt related to those long-term debt obligations at December 31, 2018 and 2017, was approximately 4.2% and 3.9%, respectively.

During the year ended December 31, 2018, the Company used $43.5 million in cash to extinguish $43.5 million in debt early. The payment did not result in a pre-tax gain or loss in the consolidated statements of comprehensive income (loss). The Company did not extinguish any debt early during 2017. During the year ended December 31, 2016, the Company used $16.5 million in cash to extinguish $18.4 million in debt early. The payment resulted in a pre-tax gain of $1.3 million, reflected as other income in the consolidated statements of comprehensive income (loss).

The aggregate amounts of principal maturities of long‑term debt as of December 31, 2018 were as follows (in thousands):


2019	$	354,072
2020		351,738
2021		347,835
2022		353,935
2023		359,677
Thereafter		1,418,181
	$	3,185,438

As of December 31, 2018 and 2017, SkyWest Airlines had a $75 million line of credit. The line of credit includes minimum liquidity and profitability covenants and is secured by certain assets. As of December 31, 2018 and 2017, SkyWest Airlines had no amount outstanding under the facility. However, at December 31, 2018 and 2017 the Company had $9.7 million and $14.8 million, respectively, in letters of credit issued under the facility which reduced the amount available under the facility to $65.3 million and $60.2 million, respectively. The facility expires on September 1, 2021 and has a variable interest rate of LIBOR plus 2.5% at December 31, 2018.

As of December 31, 2018 and 2017, the Company had $78.7 million and $87.4 million, respectively, in letters of credit and surety bonds outstanding with various banks and surety institutions in addition to the letters of credit outstanding under the line of credit.