Note 2 - Acquisitions (Details)			9 Months Ended
	Apr. 28, 2015 USD ($) shares	Feb. 27, 2015 USD ($) shares	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Note 2 - Acquisitions (Details) [Line Items]
Deposits			$ 6,089,800,000	$ 3,860,718,000
Goodwill			314,282,000	$ 108,095,000
Liberty Bancshares, Inc. [Member]
Note 2 - Acquisitions (Details) [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares (in Shares) | shares		5,181,337
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned		$ 212,200,000
Number of Bank Branches		23
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		$ 1,065,541,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share		780,658,000
Deposits		874,700,000
Goodwill		$ 95,608,000
Business Combination, Percentage of Fair Value Adjustment, Deferred Tax Asset		39.225%
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual			33,300,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual			16,300,000
Community First Bancshares, Inc. [Member]
Note 2 - Acquisitions (Details) [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares (in Shares) | shares		6,552,915
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned		$ 268,300,000
Number of Bank Branches		33
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share		$ 1,100,000,000
Deposits		1,500,000,000
Goodwill		$ 111,300,000
Business Combination, Percentage of Fair Value Adjustment, Deferred Tax Asset		39.225%
Payments to Acquire Businesses, Gross		$ 9,974
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets, Net		1,900,000,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual			58,200,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual			23,300,000
Community First Bancshares, Inc. [Member] | Preferred Stock [Member]
Note 2 - Acquisitions (Details) [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned		$ 30,900,000
Community First Bancshares, Inc. [Member] | Acquisition-related Costs Excluded [Member]
Note 2 - Acquisitions (Details) [Line Items]
Revenues			$ 7,400,000
OTIC and TCO [Member]
Note 2 - Acquisitions (Details) [Line Items]
Assets under Management, Carrying Amount	$ 1,000,000,000
Number of Investment in Shares, Repurchased Through Acquisition (in Shares) | shares	1,000
OTIC and TCO [Member] | Pending Acquisition [Member]
Note 2 - Acquisitions (Details) [Line Items]
Payments to Acquire Businesses, Gross	$ 701.9268
Conversion of Stock, Shares Converted (in Shares) | shares	16.7205
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	$ 23,600,000