Note 4 - Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Loans	$ 6,225,000,000	$ 5,633,000,000
Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing	281,000	300,000
Past Due	51,036,000	40,313,000
Current	4,949,536,000	4,286,894,000
Loans	5,000,572,000	4,327,207,000
Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	21,094,000	18,605,000
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	29,942,000	21,708,000
Consumer Portfolio Segment [Member]
Loans	543,089,000	488,563,000
Consumer Portfolio Segment [Member] | Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing	281,000	286,000
Past Due	6,213,000	5,804,000
Current	536,876,000	482,759,000
Loans	543,089,000	488,563,000
Consumer Portfolio Segment [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	3,869,000	4,502,000
Consumer Portfolio Segment [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	2,344,000	1,302,000
Consumer Portfolio Segment [Member] | Credit Card Receivable [Member]
Loans	176,953,000	184,591,000
Consumer Portfolio Segment [Member] | Credit Card Receivable [Member] | Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing	271,000	275,000
Past Due	1,133,000	991,000
Current	175,820,000	183,600,000
Loans	176,953,000	184,591,000
Consumer Portfolio Segment [Member] | Credit Card Receivable [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	568,000	716,000
Consumer Portfolio Segment [Member] | Credit Card Receivable [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	565,000	275,000
Consumer Portfolio Segment [Member] | Other Loans [Member]
Loans	366,136,000	303,972,000
Consumer Portfolio Segment [Member] | Other Loans [Member] | Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing	10,000	11,000
Past Due	5,080,000	4,813,000
Current	361,056,000	299,159,000
Loans	366,136,000	303,972,000
Consumer Portfolio Segment [Member] | Other Loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	3,301,000	3,786,000
Consumer Portfolio Segment [Member] | Other Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	1,779,000	1,027,000
Commercial Real Estate Portfolio Segment [Member]
Loans	3,562,015,000	3,028,079,000
Commercial Real Estate Portfolio Segment [Member] | Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing		14,000
Past Due	26,810,000	25,837,000
Current	3,535,205,000	3,002,242,000
Loans	3,562,015,000	3,028,079,000
Commercial Real Estate Portfolio Segment [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	9,764,000	11,942,000
Commercial Real Estate Portfolio Segment [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	17,046,000	13,895,000
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member]
Loans	457,896,000	336,759,000
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member] | Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing
Past Due	2,698,000	2,666,000
Current	455,198,000	334,093,000
Loans	457,896,000	336,759,000
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	950,000	1,420,000
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	1,748,000	1,246,000
Commercial Real Estate Portfolio Segment [Member] | Single Family Residential Loans [Member]
Loans	1,014,412,000	904,245,000
Commercial Real Estate Portfolio Segment [Member] | Single Family Residential Loans [Member] | Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing		14,000
Past Due	11,185,000	12,237,000
Current	1,003,227,000	892,008,000
Loans	1,014,412,000	904,245,000
Commercial Real Estate Portfolio Segment [Member] | Single Family Residential Loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	5,429,000	6,310,000
Commercial Real Estate Portfolio Segment [Member] | Single Family Residential Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	5,756,000	5,927,000
Commercial Real Estate Portfolio Segment [Member] | Other Commercial Loans [Member]
Loans	2,089,707,000	1,787,075,000
Commercial Real Estate Portfolio Segment [Member] | Other Commercial Loans [Member] | Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing
Past Due	12,927,000	10,934,000
Current	2,076,780,000	1,776,141,000
Loans	2,089,707,000	1,787,075,000
Commercial Real Estate Portfolio Segment [Member] | Other Commercial Loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	3,385,000	4,212,000
Commercial Real Estate Portfolio Segment [Member] | Other Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	9,542,000	6,722,000
Commercial Portfolio Segment [Member]
Loans	870,277,000	789,903,000
Commercial Portfolio Segment [Member] | Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing
Past Due	18,013,000	8,672,000
Current	852,264,000	781,231,000
Loans	870,277,000	789,903,000
Commercial Portfolio Segment [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	7,461,000	2,161,000
Commercial Portfolio Segment [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	10,552,000	6,511,000
Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	678,932,000	639,525,000
Commercial Portfolio Segment [Member] | Commercial Loans [Member] | Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing
Past Due	15,951,000	7,336,000
Current	662,981,000	632,189,000
Loans	678,932,000	639,525,000
Commercial Portfolio Segment [Member] | Commercial Loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	7,408,000	2,040,000
Commercial Portfolio Segment [Member] | Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	8,543,000	5,296,000
Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans	191,345,000	150,378,000
Commercial Portfolio Segment [Member] | Agricultural Loans [Member] | Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing
Past Due	2,062,000	1,336,000
Current	189,283,000	149,042,000
Loans	191,345,000	150,378,000
Commercial Portfolio Segment [Member] | Agricultural Loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	53,000	121,000
Commercial Portfolio Segment [Member] | Agricultural Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	2,009,000	1,215,000
Unallocated Financing Receivables [Member]
Loans	25,191,000	20,662,000
Unallocated Financing Receivables [Member] | Loans, Excluding Acquired Loans [Member]
90 Days Past Due & Accruing
Past Due
Current	25,191,000	20,662,000
Loans	25,191,000	20,662,000
Unallocated Financing Receivables [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due
Unallocated Financing Receivables [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due