Note 4 - Debt and Equity Securities (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Commitments and Contingencies (in Dollars)
Private Issue Collateralized Mortgage Obligations, Number	2
Mortgage Backed Securities Available For Sale, Amortized Cost (in Dollars)	739,357,000
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure (in Dollars)	764,701,000	720,113,000
Texas Ratio, Minimum Review Threshold	50.00%
Collateralized Mortgage Obligations [Member] | Collateralized By Commercial Real Estate [Member]
Mortgage Backed Securities Available For Sale, Amortized Cost (in Dollars)	18,000,000	15,200,000
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure (in Dollars)	18,400,000	15,700,000
Collateralized Mortgage Obligations [Member]
Number Of Instruments Below Investment Grade Evalatued For Default	5
Proceeds from Sale of Available-for-sale Securities, Debt (in Dollars)	68,500,000
Available-for-sale Securities, Gross Realized Gains (in Dollars)	3,200,000
Available-for-sale Securities, Gross Realized Losses (in Dollars)	300,000
REMIC And CMO [Member] | FHLMC [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	7
REMIC And CMO [Member] | FNMA [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	6
REMIC And CMO [Member] | Private Issue CMO [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	5
REMIC And CMO [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number Performing To Their Terms	1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number Not Performing To Their Terms	4
Underperforming Securities, Principal Loss (in Dollars)	200,000
Private Issue CMO [Member]
Number Of Instruments Below Investment Grade	5
Number Of Instruments With OTTI Charges Recorded	5
FNMA [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	9
Commitments To Purchase Available For Sale Securities [Member]
Commitments and Contingencies (in Dollars)	14,300,000
To Prepay In The Second Quarter of 2013 [Member]
Number Of Pooled Trust Securities Assumed To Prepay	2
Value Of Pooled Trust Securities Assumed To Prepay (in Dollars)	7,700,000
To Prepay In The Second Quarter of 2015 [Member]
Number Of Pooled Trust Securities Assumed To Prepay	2
Value Of Pooled Trust Securities Assumed To Prepay (in Dollars)	$ 21,500,000
Single Issuer [Member] | Trust Preferred Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1
Pooled Issuer [Member] | Trust Preferred Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	2
Collateralized By Commercial Real Estate [Member]
Private Issue Collateralized Mortgage Obligations, Number		2
Corporate Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1
Municipal [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	8
Trust Preferred Securities [Member]
Number Of Instruments Below Investment Grade	6
Number Of Instruments Carried Under Fair Value Option Below Investment Grade	2
Number Of Instruments Below Investment Grade Evalatued For Default	4
Pooled Trust Preferred Securities [Member]
Number Of Instruments On Non Accrual Status	1
Number Of Instruments With OTTI Charges Recorded	2