Note 7 - Credit Losses (Details Textual) - USD ($) $ in Thousands	Jan. 01, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance		$ 555,875	$ 571,090	$ 572,395	$ 610,243	$ 571,522	$ 551,611
Retained Earnings [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance		$ 240,989	$ 258,972	$ 259,903	$ 237,369	$ 196,583	$ 182,148
Retained Earnings [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance	$ 3,298
Income Tax Effects Allocated Directly to Equity, Cumulative Effect of Change in Accounting Principle	$ 1,109