Debt (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of Long-term Debt Instruments

(Dollars in thousands)	2017			2016
Term loans	$	343,500		$	349,500
Senior notes		150,000			150,000
Revenue bonds		65,735			65,735
Medium-term notes		17,250			22,250
Long-term principal		576,485			587,485
Interest rate swaps		(373	)		247
Debt issuance costs		(2,321	)		(3,015	)
Unamortized discounts		(472	)		(729	)
Total long-term debt (includes current portion)		573,319			583,988
Less current portion of long-term debt		(14,263	)		(11,032	)
Long-term debt	$	559,056		$	572,956

Schedule of Maturities of Long-term Debt

Scheduled principal payments due on long-term debt as of December 31, 2017 are as follows:

(Dollars in thousands)
2018	$	14,250
2019		190,000
2020		46,000
2021		40,000
2022		43,000
Thereafter		243,235
Total	$	576,485