Note 14 - Benefit Plans (Details Textual)	12 Months Ended
	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)
Defined Contribution Plan, Employer Matching Contribution, Percent of Match		4.00%
Defined Contribution Plan, Cost	$ 1,500,000	$ 1,200,000	$ 1,100,000
Annuity Payment, Maximum Contractual Term (Year)	10 years
Retirement Age to Be Attained to Receive Postretirement Benefits	65
Liability, Defined Benefit Pension Plan	$ 1,100,000	1,100,000
Pension and Other Postretirement Benefits Cost (Reversal of Cost), Total	$ 6,000	16,000	18,000
Deferred Compensation Plan, Benefits, Number of Years to Vest (Year)	3 years
Deferred Compensation Plan, Shares Acquired (in shares) | shares	0
Deferred Compensation Plan, Amount Vested	$ 1,400,000	1,300,000
Deferred Compensation Arrangement With Individual, Expense Reduction	$ 10,000	$ 2,000	$ 15,000
Deferred Compensation Plan, Shares Held (in shares) | shares	25,437	25,437
Other Assets [Member]
Cash Surrender Value of Life Insurance	$ 2,600,000	$ 2,600,000
Minimum [Member]
Annual Annuity Payments	15,000
Maximum [Member]
Annual Annuity Payments	$ 25,000