Note 5 - Loans Receivable (Details Textual)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Oct. 01, 2015 USD ($)	Jun. 13, 2014 USD ($)
Additions [Member]
Financing Receivable, Modifications, Number of Contracts		0		0
Purchased Credit Impaired [Member]
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	$ 1,500,000		$ 1,500,000		$ 1,000,000
Non PCI Loans [Member]
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing					$ 451,000
Financing Receivable Recorded Investment 90 Days Past Due and Still Accruing Number of Loans					2
Serviced for Others [Member]
Financing Receivable, Gross	15,200,000		15,200,000		$ 20,400,000
Federal Home Loan Bank of Dallas [Member]
Loans Pledged as Collateral	29,400,000		$ 29,400,000		$ 33,100,000
First National Security Company [Member]
Business Combination, Acquired Receivables, Fair Value							$ 583,600,000
Business Combination, Acquired Receivables, Gross Contractual Amount							595,100,000
Business Combination Acquired Receivables Discount							11,500,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net							21,100,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Outstanding Balance							26,900,000
Certain Loans Acquired in Transfer not Accounted for as Debt Securities Discount							$ 5,800,000
Acquisition of MNB [Member]
Business Combination, Acquired Receivables, Fair Value						$ 364,500,000
Business Combination, Acquired Receivables, Gross Contractual Amount						375,000,000
Business Combination Acquired Receivables Discount						$ 10,500,000
Nonaccrual [Member]
Financing Receivable, Modifications, Number of Contracts			13		14
Financing Receivable, Modifications, Recorded Investment	1,248,000		$ 1,248,000		$ 1,429,000
Mortgage Loans in Process of Foreclosure, Amount	$ 2,000,000		$ 2,000,000		$ 1,800,000
Financing Receivable, Modifications, Number of Contracts	1		16		17
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	0	0	0
Financing Receivable, Gross	$ 1,482,712,000		$ 1,482,712,000		$ 1,458,094,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	15,039,000	$ 17,858,000	15,039,000	$ 17,858,000	16,347,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Outstanding Balance	19,313,000	$ 20,913,000	19,313,000	$ 20,913,000	20,289,000
Financing Receivable, Modifications, Recorded Investment	1,527,000		1,527,000		$ 1,713,000
Minimum Loan Amount for Loans Analyzed by Credit Risk	$ 500,000		$ 500,000