Financial Instruments (Estimated Fair Values Of Financial Instruments) (Details) - USD ($) $ in Thousands		Dec. 31, 2016		Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Feb. 29, 2016	Dec. 31, 2015		Dec. 31, 2014	[1]	Dec. 31, 2013	[1]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents, Carrying Amount		$ 82,584	[1],[2]	$ 72,855	$ 65,378	$ 7,824		$ 7,925	[1],[2]	$ 24,017		$ 49,032
Long-term debt, including current portion, Carrying Amount	[3]	(586,756)						(606,337)
Company owned life insurance (COLI), Carrying Amount		70						687
Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents, Fair Value		82,584						7,925
Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current portion, Fair Value	[3]	(601,290)						(625,440)
Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Company owned life insurance (COLI), Fair Value		70						687
Term loans, variable rate 2.50% to 3.00% due 2019 through 2026 and fixed rate 2.95% to 4.64% due 2017 through 2024 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current portion, Carrying Amount		(349,500)					$ (27,500)	(322,000)
Term loans, variable rate 2.50% to 3.00% due 2019 through 2026 and fixed rate 2.95% to 4.64% due 2017 through 2024 [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current portion, Fair Value		(350,909)						(322,000)
Senior notes, 7.50%, due 2019 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current portion, Carrying Amount		(149,271)						(149,013)
Senior notes, 7.50%, due 2019 [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current portion, Fair Value		(164,250)						(165,375)
Revenue bonds, 2.75% due 2024 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current portion, Carrying Amount		(65,735)						(108,074)
Revenue bonds, 2.75% due 2024 [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current portion, Fair Value		(62,205)						(108,454)
Medium-term notes, 8.75% to 8.89%, due 2017 through 2022 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current portion, Carrying Amount		(22,250)						(27,250)
Medium-term notes, 8.75% to 8.89%, due 2017 through 2022 [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current portion, Fair Value		(23,926)						(29,611)
Interest rate contracts [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Derivative assets related to interest rate swaps, Carrying Amount		1,395						581
Derivative liabilities related to interest rate swaps, Carrying Amount		(91)
Interest rate contracts [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Derivative assets related to interest rate swaps, Fair Value		1,395						$ 581
Derivative liabilities related to interest rate swaps, Fair Value		$ (91)

[1] Certain short-term investments in 2015 and 2014 were reclassified to cash and cash equivalents to conform with the 2016 presentation.

[2] Short-term investments as of December 31, 2015 were reclassified to cash and cash equivalents to conform with the 2016 presentation.

[3] The carrying amount of long-term debt includes principal and unamortized discounts.