Debt (Tables)

12 Months Ended

Dec. 31, 2015

Debt Disclosure [Abstract]

Schedule of Long-term Debt Instruments

(Dollars in thousands)	2015			2014
Term loans, variable rate 1.98% to 2.23% due 2019 through 2021 and fixed rate 2.95% to 4.64% due 2017 through 2024	$	322,000		$	322,000
Senior notes, 7.50%, due 2019	150,000			150,000
Revenue bonds, 5.90% to 6.95%, due 2024 and 2026	108,335			108,335
Debentures, 6.95%, due 2015	—			22,500
Medium-term notes, 8.75% to 8.89%, due 2016 through 2022	27,250			27,250
	607,585			630,085
Interest rate swaps (See Note 10: Financial Instruments)	581			793
Less debt issuance costs	(3,037		)	(3,675		)
Less unamortized discounts	(1,248		)	(1,535		)
Total long-term debt (includes current portion)	603,881			625,668
Less current portion of long-term debt	(5,007		)	(22,870		)
Long-term debt	$	598,874		$	602,798

Schedule of Maturities of Long-term Debt

Scheduled principal payments due on long-term debt subsequent to December 31, 2015, are as follows:

(Dollars in thousands)
2016	$	5,000
2017	11,000
2018	14,250
2019	190,000
2020	46,000
Thereafter	341,335
Total	$	607,585