Note 8 - Credit Losses (Details Textual) - USD ($) $ in Thousands	Jan. 01, 2020	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance		$ 484,580	$ 592,733	$ 583,065	$ 553,519	$ 552,728	$ 555,875	$ 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		$ 163,637	$ 277,426	$ 273,254	$ 246,850	$ 233,765	$ 240,989	$ 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