Financial Commitments (Long-Term Debt) (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Total debt	$ 823,448,000	$ 865,359,000
Less - current maturities	(88,917,000)	(81,292,000)
Long-term debt, net	734,531,000	784,067,000
Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Face amount	300,000,000	300,000,000
Unamortized discount	933,000	1,223,000
Total debt	299,067,000	298,777,000
Original Revolver [Member]
Debt Instrument [Line Items]
Total debt	158,000,000	130,000,000
Term Loan [Member]
Debt Instrument [Line Items]
Total debt	223,750,000	242,500,000
Equipment Financing, Mortgages And Acquisition-Related Notes [Member]
Debt Instrument [Line Items]
Total debt	133,288,000	183,202,000
Other Indebtedness [Member]
Debt Instrument [Line Items]
Total debt	$ 9,343,000	$ 10,880,000