Note 6 - Senior Notes, Credit Facility and Capital Leases - Credit Facility (Details)	12 Months Ended
	Dec. 31, 2017
Maximum [Member]
Senior leverage ratio (debt secured by liens/EBITDA)	2.5
Leverage ratio (total debt less unencumbered cash/EBITDA)	4
Interest coverage ratio (EBITDA/interest expense)	3
New Facility [Member]
Standby fee per annum on undrawn amounts	0.50%
New Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Variable rate	2.25%
New Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]
Variable rate	3.25%
New Facility [Member] | Base Rate [Member] | Minimum [Member]
Variable rate	1.25%
New Facility [Member] | Base Rate [Member] | Maximum [Member]
Variable rate	2.25%