Note 10 - Fair Value Measurement - Cash and Cash Equivalents (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Commodity swap	$ 209
Total assets	80,702	$ 100,531	$ 74,237
Interest rate swap	8,353	4,603	5,564
Total liabilities	8,353	4,603	5,564
Fair Value, Inputs, Level 1 [Member]
Commodity swap	0
Total assets	80,493	100,531	74,237
Interest rate swap	0	0	0
Total liabilities	0	0	0
Fair Value, Inputs, Level 2 [Member]
Commodity swap	209
Total assets	209	0	0
Interest rate swap	8,353	4,603	5,564
Total liabilities	8,353	4,603	5,564
Fair Value, Inputs, Level 3 [Member]
Commodity swap	0
Total assets	0	0	0
Interest rate swap	0	0	0
Total liabilities	0	0	0
Money Market Funds [Member]
Cash equivalents	78,981	94,696	68,579
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Cash equivalents	78,981	94,696	68,579
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Cash equivalents	0	0	0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Cash equivalents	0	0	0
Restricted Cash [Member]
Other noncurrent assets	1,512	5,835	5,658
Restricted Cash [Member] | Fair Value, Inputs, Level 1 [Member]
Other noncurrent assets	1,512	5,835	5,658
Restricted Cash [Member] | Fair Value, Inputs, Level 2 [Member]
Other noncurrent assets	0	0	0
Restricted Cash [Member] | Fair Value, Inputs, Level 3 [Member]
Other noncurrent assets	$ 0	$ 0	$ 0