Note 7 - Fair Value of Financial Instruments (Detail) - Carrying Values and Fair Values of Financial Assets and Liabilities (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financial Assets:
Cash	$ 28,060	$ 36,316
Cash	28,060	36,316
Cash collateral posted	547	273
Accrued interest receivable	2,713	2,759
Accrued interest receivable	2,713	2,759
Financial Liabilities:
Repurchase agreements	1,108,942	1,135,830
Repurchase agreements	1,108,942	1,135,830
Cash collateral held	5,782	1,426
Accrued interest payable	736	844
Accrued interest payable	736	844
Fair Value, Inputs, Level 1 [Member]
Financial Assets:
Cash	28,060	36,316
Fair Value, Inputs, Level 2 [Member]
Financial Assets:
Cash collateral posted	547	273
Accrued interest receivable	2,713	2,759
Financial Liabilities:
Repurchase agreements	1,108,942	1,135,830
Cash collateral held	5,782	1,426
Accrued interest payable	$ 736	$ 844