Long-Term Debt (Schedule of Long-Term Debt) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Mar. 31, 2013
Debt Instrument [Line Items]
Less unamortized debt issuance costs	$ (1,791)	$ (2,379)
Total debt	(210,209)	(210,021)
Less current maturities	400	400
Total long-term debt	209,809	209,621
Senior Subordinated 6.25% Notes
Debt Instrument [Line Items]
Total debt	$ (210,000)	$ (210,000)
Senior Subordinated Notes, interest rate	6.25%	6.25%	6.25%
Other debt
Debt Instrument [Line Items]
Total debt	$ (2,000)	$ (2,400)