Note 8 - Deposits - Summary of Deposits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Noninterest-bearing demand	$ 866,380,000	$ 810,600,000
Noninterest-bearing demand	34.30%	34.10%
Noninterest-bearing demand	6.90%
Interest-bearing checking	$ 387,758,000	$ 377,929,000
Interest-bearing checking	15.40%	15.90%
Interest-bearing checking	2.60%
Money market	$ 427,119,000	$ 272,051,000
Money market	16.90%	11.50%
Money market	57.00%
Savings	$ 327,530,000	$ 344,988,000
Savings	13.00%	14.50%
Savings	(5.10%)
Time, under $100,000	$ 152,294,000	$ 146,169,000
Time, under $100,000	6.00%	6.20%
Time, under $100,000	4.20%
Time, $100,000 and over	$ 361,284,000	$ 423,248,000
Total local deposits	$ 2,419,707,000	$ 2,298,795,000
Total local deposits	95.90%	96.80%
Total local deposits	5.30%
Out-of-area time, under $100,000	$ 0	$ 0
Out-of-area time, under $100,000	0.00%	0.00%
Out-of-area time, under $100,000	0.00%
Out-of-area time, $100,000 and over	$ 102,658,000	$ 76,190,000
Out-of-area time, $100,000 and over	4.10%	3.20%
Out-of-area time, $100,000 and over	34.70%
Total out-of-area deposits	$ 102,658,000	$ 76,190,000
Total out-of-area deposits	4.10%	3.20%
Total out-of-area deposits	34.70%
Total deposits	$ 2,522,365,000	$ 2,374,985,000
Total deposits	100.00%	100.00%
Total deposits	6.20%
Geographic Distribution, Domestic [Member]
Time, $100,000 and over	$ 258,626,000	$ 347,058,000
Time, $100,000 and over	10.30%	14.60%
Time, $100,000 and over	(25.50%)