Note 5 - Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Loans	$ 6,303,000,000	$ 5,633,000,000
Loans, Excluding Acquired Loans [Member]
Past Due	46,781,000	40,313,000
Current	5,164,531,000	4,286,894,000
Loans	5,211,312,000	4,327,207,000
90 Days Past Due & Accruing	232,000	300,000
Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	15,973,000	18,605,000
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	30,808,000	21,708,000
Consumer Portfolio Segment [Member]
Loans	494,262,000	488,563,000
Consumer Portfolio Segment [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	8,587,000	5,804,000
Current	485,675,000	482,759,000
Loans	494,262,000	488,563,000
90 Days Past Due & Accruing	222,000	286,000
Consumer Portfolio Segment [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	5,525,000	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	3,062,000	1,302,000
Consumer Portfolio Segment [Member] | Credit Card Receivable [Member]
Loans	176,316,000	184,591,000
Consumer Portfolio Segment [Member] | Credit Card Receivable [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	1,147,000	991,000
Current	175,169,000	183,600,000
Loans	176,316,000	184,591,000
90 Days Past Due & Accruing	218,000	275,000
Consumer Portfolio Segment [Member] | Credit Card Receivable [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	655,000	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	492,000	275,000
Consumer Portfolio Segment [Member] | Other Loans [Member]
Loans	317,946,000	303,972,000
Consumer Portfolio Segment [Member] | Other Loans [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	7,440,000	4,813,000
Current	310,506,000	299,159,000
Loans	317,946,000	303,972,000
90 Days Past Due & Accruing	4,000	11,000
Consumer Portfolio Segment [Member] | Other Loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	4,870,000	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	2,570,000	1,027,000
Commercial Real Estate Portfolio Segment [Member]
Loans	3,794,900,000	3,028,079,000
Commercial Real Estate Portfolio Segment [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	24,196,000	25,837,000
Current	3,770,704,000	3,002,242,000
Loans	3,794,900,000	3,028,079,000
90 Days Past Due & Accruing		14,000
Commercial Real Estate Portfolio Segment [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	8,988,000	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	15,208,000	13,895,000
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member]
Loans	515,274,000	336,759,000
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	1,918,000	2,666,000
Current	513,356,000	334,093,000
Loans	515,274,000	336,759,000
90 Days Past Due & Accruing
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	440,000	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	1,478,000	1,246,000
Commercial Real Estate Portfolio Segment [Member] | Single Family Residential Loans [Member]
Loans	1,048,403,000	904,245,000
Commercial Real Estate Portfolio Segment [Member] | Single Family Residential Loans [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	10,301,000	12,237,000
Current	1,038,102,000	892,008,000
Loans	1,048,403,000	904,245,000
90 Days Past Due & Accruing		14,000
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	5,516,000	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	4,785,000	5,927,000
Commercial Real Estate Portfolio Segment [Member] | Other Commercial Loans [Member]
Loans	2,231,223,000	1,787,075,000
Commercial Real Estate Portfolio Segment [Member] | Other Commercial Loans [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	11,977,000	10,934,000
Current	2,219,246,000	1,776,141,000
Loans	2,231,223,000	1,787,075,000
90 Days Past Due & Accruing
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	3,032,000	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	8,945,000	6,722,000
Commercial Portfolio Segment [Member]
Loans	896,809,000	789,903,000
Commercial Portfolio Segment [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	13,998,000	8,672,000
Current	882,811,000	781,231,000
Loans	896,809,000	789,903,000
90 Days Past Due & Accruing	10,000
Commercial Portfolio Segment [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	1,460,000	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	12,538,000	6,511,000
Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	688,960,000	639,525,000
Commercial Portfolio Segment [Member] | Commercial Loans [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	11,736,000	7,336,000
Current	677,224,000	632,189,000
Loans	688,960,000	639,525,000
90 Days Past Due & Accruing	10,000
Commercial Portfolio Segment [Member] | Commercial Loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	991,000	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	10,745,000	5,296,000
Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans	207,849,000	150,378,000
Commercial Portfolio Segment [Member] | Agricultural Loans [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	2,262,000	1,336,000
Current	205,587,000	149,042,000
Loans	207,849,000	150,378,000
90 Days Past Due & Accruing
Commercial Portfolio Segment [Member] | Agricultural Loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member] | Loans, Excluding Acquired Loans [Member]
Past Due	469,000	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	1,793,000	1,215,000
Unallocated Financing Receivables [Member]
Loans	25,341,000	20,662,000
Unallocated Financing Receivables [Member] | Loans, Excluding Acquired Loans [Member]
Past Due
Current	25,341,000	20,662,000
Loans	25,341,000	20,662,000
90 Days Past Due & Accruing
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