Debt and Other Obligations

As of March 31, 2017, the Company held non-public and public debt instruments.

Long-term debt is comprised of the following:



	As of				Three Months Ended March 31,
	March 31, 2017		December 31, 2016		2017		2016
	(in millions)				(weighted-average interest rates)
Fixed-rate senior term loans due through 2027	$	443.4	$	451.9	4.10	%	4.10	%
Fixed-rate junior term loans due through 2022	45.2		47.1		6.90	%	6.90	%
Fixed-rate loans due through 2029	77.0		—		3.88	%	N/A
Fixed-rate class A enhanced equipment trust certificates due through 2028	440.2		409.8		4.10	%	4.03	%
Fixed-rate class B enhanced equipment trust certificates due through 2024	111.8		103.6		4.45	%	4.37	%
Long-term debt	$	1,117.6	$	1,012.4
Less current maturities	92.7		84.4
Less unamortized discounts	33.2		30.6
Total	$	991.7	$	897.4

During the three months ended March 31, 2017 and March 31, 2016, the Company made scheduled principal payments of $10.2 million and $9.7 million, respectively, on its outstanding debt obligations.

At March 31, 2017, long-term debt principal payments for the next five years and thereafter are as follows:



	March 31, 2017
	(in millions)
Remainder of 2017	$	85.8
2018	90.0
2019	88.4
2020	87.0
2021	85.7
2022 and beyond	680.7
Total debt principal payments	$	1,117.6

Interest Expense

Interest expense related to long-term debt consisted of the following:



	Three Months Ended March 31,
	2017		2016
	(in thousands)
Senior term loans	$	4,672	$	5,048
Junior term loans	803		937
Fixed-rate loans	159		—
Class A enhanced equipment trust certificates	4,308		1,183
Class B enhanced equipment trust certificates	1,185		336
Commitment fees	30		35
Amortization of debt discounts	1,231		516
Total	$	12,388	$	8,055