Note 7 - Credit Losses (Details Textual) - USD ($) $ in Thousands	Jan. 01, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance		$ 672,813	$ 553,519	$ 572,395	$ 551,611
Accounts Receivable, Allowance for Credit Loss, Ending Balance	$ 2,811
Other Non-trade Contractual Arrangements [Member]
Accounts Receivable, before Allowance for Credit Loss		8,263	5,097
Accounts Receivable, Allowance for Credit Loss, Ending Balance	711	6,948	3,524
Other Non-trade Contractual Arrangements [Member] | Other Receivables [Member]
Accounts Receivable, Allowance for Credit Loss, Ending Balance		12,329	6,960
Other Non-trade Contractual Arrangements [Member] | Other Assets [Member]
Accounts Receivable, Allowance for Credit Loss, Ending Balance		2,882	1,661
Cumulative Effect, Period of Adoption, Adjustment [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance				(3,298)
Accounts Receivable, Allowance for Credit Loss, Ending Balance	4,407
Cumulative Effect, Period of Adoption, Adjustment [Member] | Other Non-trade Contractual Arrangements [Member]
Accounts Receivable, Allowance for Credit Loss, Ending Balance	3,456
Retained Earnings [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance		$ 280,960	$ 246,850	259,903	$ 182,148
Retained Earnings [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance	3,298			$ (3,298)
Income Tax Effects Allocated Directly to Equity, Cumulative Effect of Change in Accounting Principle	$ 1,109