Note 8 - Credit Losses (Details Textual) - USD ($) $ in Thousands	Jan. 01, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance		$ 583,065	$ 553,519	$ 571,090	$ 572,395
Cumulative Effect, Period of Adoption, Adjustment [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance					(3,298)
Retained Earnings [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance		$ 273,254	$ 246,850	$ 258,972	259,903
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