Note 9 - Share-based Compensation and Cash-based Incentive Compensation - Summary of Compensation Expense Related to Share-Based Awards and Cash-Based Awards (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based compensation		$ 1,248	$ 1,373	$ 2,429	$ 3,808
Total charged to operating income		3,599	3,744	8,397	11,645
General and Administrative Expense [Member]
Share-based compensation		1,248	1,373	2,429	3,808
Lease operating expense (1)	[1]	1,679	1,534	5,017	5,597
Lease Operating Expense [Member]
Lease operating expense (1)	[1]	$ 672	$ 837	$ 951	$ 2,240

[1] Includes adjustments of accruals to actual payments.