Long-Term Debt (Schedule Of Long-Term Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Revolving credit facility	$ 95,000	$ 104,111
Equipment notes payable	2,318	2,680
Notes payable	13,296	14,438
Line of credit, senior note payable, equipment notes payable and senior note	431,671	394,227
Current portion of equipment note payable	(1,546)	(1,320)
Current portion of note payable	(1,212)	(1,145)
Capital leases (included in other long term liabilities)	(772)	(1,360)
Long term debt	428,141	390,402
8.000% Senior Notes Due in 2022 [Member]
Debt Instrument [Line Items]
Senior notes	$ 321,057
7.375% Senior Notes Due In 2019 [Member]
Debt Instrument [Line Items]
Senior notes		$ 272,998