Financial Commitments (Long-Term Debt) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total debt	$ 898,626	$ 761,504
Less: Current maturities	11,921	16,767
Long-term debt, net	886,705	744,737
Convertible Notes [Member]
Debt Instrument [Line Items]
Total debt	174,089	171,481
Equipment Financing And Mortgages [Member]
Debt Instrument [Line Items]
Total debt	46,454	50,904
Other Indebtedness [Member]
Debt Instrument [Line Items]
Total debt	2,857	4,598
2017 Senior Notes [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	493,726	493,521
2017 Credit Facility [Member] | Credit Facility [Member]
Debt Instrument [Line Items]
Total debt	$ 181,500	$ 41,000