Note 2 - Acquisitions (Details Textual)							12 Months Ended
		Sep. 09, 2016 USD ($) shares	Oct. 29, 2015 USD ($) shares	Feb. 28, 2015 shares	Feb. 27, 2015 USD ($) shares	Aug. 31, 2014 USD ($) shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($)	Oct. 28, 2015 USD ($)
Goodwill							$ 327,686,000		$ 348,505,000
Business Percentage of Fair Value Adjustment Deferred Tax Asset									39.225%
Citizens National Bank [Member]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares		835,741
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned		$ 41,300,000
Payments to Acquire Businesses, Gross		$ 35,000,000
Number of Bank Branches		9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		$ 585,500,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share		340,850,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits		509,857,000
Goodwill		$ 21,495,000
Liberty Bancshares, Inc. [Member]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares					5,181,337
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned					$ 212,200,000
Number of Bank Branches					24
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets					$ 1,066,272,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share					780,658,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits					874,714,000
Goodwill					$ 95,207,000
Business Acquisition, Pro Forma Revenue							46,000,000
Business Acquisition, Pro Forma Net Income (Loss)							24,200,000
Community First Bancshares Inc [Member]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares					6,552,915
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned					$ 268,300,000
Payments to Acquire Businesses, Gross					$ 9,974
Number of Bank Branches					33
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets					$ 1,915,061,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share					1,136,543,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits					1,536,062,000
Goodwill					$ 110,440,000
Business Acquisition, Pro Forma Revenue							77,300,000
Business Acquisition, Pro Forma Net Income (Loss)							33,300,000
Community First Bancshares Inc [Member] | Preferred Stock [Member]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares					30,852
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned					$ 30,900,000
Liberty and Community First [Member]
Business Combination, Acquisition Related Costs							7,400,000
Business Acquisition, Pro Forma Revenue	[1]						395,959,000	$ 390,606,000
Business Acquisition, Pro Forma Net Income (Loss)							$ 85,773,000	$ 64,166,000
OTIC and TCO [Member]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares			339,290
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned			$ 17,900,000
Payments to Acquire Businesses, Gross			5,800,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			14,895,000
Goodwill			$ 13,268,000
Assets under Management, Carrying Amount										$ 1,000,000,000
Number of Investment in Shares Repurchased Through Acquisition | shares				1,000
Delta Trust [Member]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares						1,629,515
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned						$ 65,000,000
Payments to Acquire Businesses, Gross						$ 2,400,000
Number of Bank Branches						9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets						$ 417,386,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Acquired Not Covered by FDIC Loss Share						311,680,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Total Deposits						355,362,000
Goodwill						$ 29,022,000

[1] Net interest income plus noninterest income.