Note 2 - Acquisitions - Assets Acquired and Liabilities Assumed (Details) - USD ($)	Sep. 09, 2016	Oct. 29, 2015	Feb. 27, 2015	Aug. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Goodwill					$ 348,505,000	$ 327,686,000
Citizens National Bank [Member]
Cash and due from banks	$ 131,467,000
Federal funds sold	10,000,000
Investment securities	61,988,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share	340,850,000
Allowance for loan losses
Foreclosed assets	3,442,000
Premises and equipment	8,085,000
Bank owned life insurance	6,632,000
Core deposit intangible	5,075,000
Other intangibles	591,000
Other assets	17,370,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	585,500,000
Non-interest bearing transaction accounts	109,281,000
Interest bearing transaction accounts and savings deposits	204,912,000
Time deposits	195,664,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits	509,857,000
Securities sold under agreement to repurchase	13,233,000
FHLB borrowings	4,047,000
Accrued interest and other liabilities	3,558,000
Total liabilities assumed	530,695,000
Equity
Total liabilities and equity assumed	530,695,000
Net assets acquired	54,805,000
Business Combination, Consideration Transferred	76,300,000
Goodwill	21,495,000
Citizens National Bank [Member] | Cost Acquired [Member]
Cash and due from banks	131,467,000
Federal funds sold	10,000,000
Investment securities	61,987,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share	350,361,000
Allowance for loan losses	(4,313,000)
Foreclosed assets	4,960,000
Premises and equipment	6,746,000
Bank owned life insurance	6,632,000
Core deposit intangible
Other intangibles
Other assets	17,364,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	585,204,000
Non-interest bearing transaction accounts	109,281,000
Interest bearing transaction accounts and savings deposits	204,912,000
Time deposits	195,664,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits	509,857,000
Securities sold under agreement to repurchase	13,233,000
FHLB borrowings	4,000,000
Accrued interest and other liabilities	3,558,000
Total liabilities assumed	530,648,000
Equity	54,556,000
Total liabilities and equity assumed	585,204,000
Citizens National Bank [Member] | Fair Value Adjustments [Member]
Cash and due from banks
Federal funds sold
Investment securities	1,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share	(9,511,000)
Allowance for loan losses	4,313,000
Foreclosed assets	(1,518,000)
Premises and equipment	1,339,000
Bank owned life insurance
Core deposit intangible	5,075,000
Other intangibles	591,000
Other assets	6,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	296,000
Non-interest bearing transaction accounts
Interest bearing transaction accounts and savings deposits
Time deposits
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits
Securities sold under agreement to repurchase
FHLB borrowings	47,000
Accrued interest and other liabilities
Total liabilities assumed	47,000
Equity	(54,556,000)
Total liabilities and equity assumed	$ (54,509,000)
Liberty Bancshares, Inc. [Member]
Federal funds sold			$ 7,060,000
Investment securities			98,788,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share			780,658,000
Allowance for loan losses
Premises and equipment			31,024,000
Bank owned life insurance			16,972,000
Core deposit intangible			14,556,000
Other intangibles
Other assets			14,591,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			1,066,272,000
Non-interest bearing transaction accounts			146,618,000
Interest bearing transaction accounts and savings deposits			543,183,000
Time deposits			184,913,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits			874,714,000
FHLB borrowings			46,351,000
Accrued interest and other liabilities			8,128,000
Total liabilities assumed			949,303,000
Equity
Total liabilities and equity assumed			949,303,000
Net assets acquired			116,969,000
Business Combination, Consideration Transferred			212,176,000
Goodwill			95,207,000
Cash and due from banks, including time deposits			102,623,000
Subordinated debentures			20,110,000
Liberty Bancshares, Inc. [Member] | Cost Acquired [Member]
Federal funds sold			7,060,000
Investment securities			99,123,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share			790,493,000
Allowance for loan losses			(10,422,000)
Premises and equipment			34,239,000
Bank owned life insurance			16,972,000
Core deposit intangible			699,000
Other intangibles			3,063,000
Other assets			17,703,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			1,061,567,000
Non-interest bearing transaction accounts			146,618,000
Interest bearing transaction accounts and savings deposits			543,183,000
Time deposits			184,913,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits			874,714,000
FHLB borrowings			46,128,000
Accrued interest and other liabilities			7,828,000
Total liabilities assumed			949,290,000
Equity			112,277,000
Total liabilities and equity assumed			1,061,567,000
Cash and due from banks, including time deposits			102,637,000
Subordinated debentures			20,620,000
Liberty Bancshares, Inc. [Member] | Fair Value Adjustments [Member]
Federal funds sold
Investment securities			(335,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share			(9,835,000)
Allowance for loan losses			10,422,000
Premises and equipment			(3,215,000)
Bank owned life insurance
Core deposit intangible			13,857,000
Other intangibles			(3,063,000)
Other assets			(3,112,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			4,705,000
Non-interest bearing transaction accounts
Interest bearing transaction accounts and savings deposits
Time deposits
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits
FHLB borrowings			223,000
Accrued interest and other liabilities			300,000
Total liabilities assumed			13,000
Equity			(112,277,000)
Total liabilities and equity assumed			(112,264,000)
Cash and due from banks, including time deposits			(14,000)
Subordinated debentures			(510,000)
Community First Bancshares Inc [Member]
Cash and due from banks			39,848,000
Federal funds sold			76,508,000
Investment securities			566,818,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share			1,136,543,000
Allowance for loan losses
Foreclosed assets			747,000
Premises and equipment			42,043,000
Bank owned life insurance			22,149,000
Core deposit intangible			11,273,000
Other intangibles			420,000
Other assets			11,474,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			1,915,061,000
Non-interest bearing transaction accounts			103,825,000
Interest bearing transaction accounts and savings deposits			995,207,000
Time deposits			437,030,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits			1,536,062,000
FHLB borrowings			143,721,000
Accrued interest and other liabilities			9,370,000
Total liabilities assumed			1,726,297,000
Equity
Total liabilities and equity assumed			1,726,297,000
Net assets acquired			188,764,000
Business Combination, Consideration Transferred			299,204,000
Goodwill			110,440,000
Subordinated debentures			20,914,000
Deferred tax asset			7,238,000
Federal funds purchased and securities sold under agreement to repurchase			16,230,000
Fed funds purchased			16,230,000
Community First Bancshares Inc [Member] | Cost Acquired [Member]
Cash and due from banks			39,848,000
Federal funds sold			76,508,000
Investment securities			570,199,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share			1,163,398,000
Allowance for loan losses			(14,635,000)
Foreclosed assets			747,000
Premises and equipment			44,837,000
Bank owned life insurance			22,149,000
Core deposit intangible
Other intangibles
Other assets			11,474,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			1,918,325,000
Non-interest bearing transaction accounts			103,825,000
Interest bearing transaction accounts and savings deposits			995,207,000
Time deposits			436,181,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits			1,535,213,000
FHLB borrowings			143,047,000
Accrued interest and other liabilities			8,769,000
Total liabilities assumed			1,725,013,000
Equity			193,312,000
Total liabilities and equity assumed			1,918,325,000
Goodwill			100,000
Subordinated debentures			21,754,000
Deferred tax asset			3,700,000
Federal funds purchased and securities sold under agreement to repurchase			16,230,000
Fed funds purchased			16,230,000
Community First Bancshares Inc [Member] | Fair Value Adjustments [Member]
Cash and due from banks
Federal funds sold
Investment securities			(3,381,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share			(26,855,000)
Allowance for loan losses			14,635,000
Foreclosed assets
Premises and equipment			(2,794,000)
Bank owned life insurance
Core deposit intangible			11,273,000
Other intangibles			420,000
Other assets
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			(3,264,000)
Non-interest bearing transaction accounts
Interest bearing transaction accounts and savings deposits
Time deposits			849,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits			849,000
FHLB borrowings			674,000
Accrued interest and other liabilities			601,000
Total liabilities assumed			1,284,000
Equity			(193,312,000)
Total liabilities and equity assumed			(192,028,000)
Goodwill			(100,000)
Subordinated debentures			(840,000)
Deferred tax asset			3,538,000
Federal funds purchased and securities sold under agreement to repurchase
Fed funds purchased
OTIC and TCO [Member]
Cash and due from banks		$ 1,756,000
Investment securities		241,000
Premises and equipment		1,544,000
Other intangibles		9,733,000
Other assets		1,621,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		14,895,000
Accrued interest and other liabilities		302,000
Total liabilities assumed		4,540,000
Equity
Total liabilities and equity assumed		4,540,000
Net assets acquired		10,355,000
Business Combination, Consideration Transferred		23,623,000
Goodwill		13,268,000
Deferred tax liability		4,238,000
OTIC and TCO [Member] | Cost Acquired [Member]
Cash and due from banks		1,756,000
Investment securities		241,000
Premises and equipment		1,126,000
Other intangibles
Other assets		752,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		3,875,000
Accrued interest and other liabilities		302,000
Total liabilities assumed		365,000
Equity		3,510,000
Total liabilities and equity assumed		3,875,000
Deferred tax liability		63,000
OTIC and TCO [Member] | Fair Value Adjustments [Member]
Cash and due from banks
Investment securities
Premises and equipment		418,000
Other intangibles		9,733,000
Other assets		869,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		11,020,000
Accrued interest and other liabilities
Total liabilities assumed		4,175,000
Equity		(3,510,000)
Total liabilities and equity assumed		665,000
Deferred tax liability		$ 4,175,000
Delta Trust [Member]
Cash and due from banks				$ 13,739,000
Investment securities				62,373,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share				311,680,000
Foreclosed assets				1,791,000
Premises and equipment				3,972,000
Bank owned life insurance				7,530,000
Core deposit intangible				4,318,000
Other intangibles				5,140,000
Other assets				4,426,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets				417,386,000
Non-interest bearing transaction accounts				63,259,000
Interest bearing transaction accounts and savings deposits				200,596,000
Time deposits				91,507,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits				355,362,000
FHLB borrowings				10,977,000
Accrued interest and other liabilities				1,528,000
Total liabilities assumed				378,967,000
Equity
Total liabilities and equity assumed				378,967,000
Net assets acquired				38,419,000
Business Combination, Consideration Transferred				67,441,000
Goodwill				29,022,000
Deferred tax asset				2,417,000
Federal funds purchased and securities sold under agreement to repurchase				11,100,000
Fed funds purchased				11,100,000
Delta Trust [Member] | Cost Acquired [Member]
Cash and due from banks				13,739,000
Investment securities				62,410,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share				326,829,000
Allowance for loan losses				(6,008,000)
Foreclosed assets				3,262,000
Premises and equipment				4,405,000
Bank owned life insurance				7,530,000
Core deposit intangible
Other intangibles				137,000
Other assets				5,807,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets				420,792,000
Non-interest bearing transaction accounts				63,259,000
Interest bearing transaction accounts and savings deposits				200,596,000
Time deposits				91,507,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits				355,362,000
FHLB borrowings				11,106,000
Accrued interest and other liabilities				1,528,000
Total liabilities assumed				379,096,000
Equity				41,696,000
Total liabilities and equity assumed				420,792,000
Goodwill				822,000
Deferred tax asset				1,859,000
Federal funds purchased and securities sold under agreement to repurchase				11,100,000
Fed funds purchased				11,100,000
Delta Trust [Member] | Fair Value Adjustments [Member]
Cash and due from banks
Investment securities				(37,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share				(15,149,000)
Allowance for loan losses				6,008,000
Foreclosed assets				(1,471,000)
Premises and equipment				(433,000)
Bank owned life insurance
Core deposit intangible				4,318,000
Other intangibles				5,003,000
Other assets				(1,381,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets				(3,406,000)
Non-interest bearing transaction accounts
Interest bearing transaction accounts and savings deposits
Time deposits
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits
FHLB borrowings				(129,000)
Accrued interest and other liabilities
Total liabilities assumed				(129,000)
Equity				(41,696,000)
Total liabilities and equity assumed				(41,825,000)
Goodwill				(822,000)
Deferred tax asset				558,000
Federal funds purchased and securities sold under agreement to repurchase
Fed funds purchased