Note 5 - Agency Securities, Available for Sale (Detail) - Unrealized Gain or Loss Position and Components of Carrying Value of Available for Sale Agency Securities (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Principal Amount	$ 1,038,268	$ 1,055,456
Net unamortized premium	60,455	61,504
Amortized cost	1,098,723	1,116,960
Unrealized gains		90
Unrealized losses	(20,442)	(4,692)
Fair value	1,078,281	1,112,358
Fannie Mae [Member]
Principal Amount	641,220	651,867
Net unamortized premium	38,020	38,683
Amortized cost	679,240	690,550
Unrealized gains		86
Unrealized losses	(11,515)	(2,480)
Fair value	667,725	688,156
Freddie Mac [Member]
Principal Amount	397,048	403,589
Net unamortized premium	22,435	22,821
Amortized cost	419,483	426,410
Unrealized gains		4
Unrealized losses	(8,927)	(2,212)
Fair value	$ 410,556	$ 424,202

Note 5 - Agency Securities, Available for Sale (Detail) - Unrealized Gain or Loss Position and Components of Carrying Value of Available for Sale Agency Securities (USD $)
In Thousands, unless otherwise specified

Mar. 31, 2013

Dec. 31, 2012

$ 1,038,268

$ 1,055,456

Net unamortized premium

60,455

61,504

Amortized cost

1,098,723

1,116,960

Unrealized gains

Unrealized losses

(20,442)

(4,692)

Fair value

1,078,281

1,112,358

Fannie Mae [Member]

Principal Amount

641,220

651,867

Net unamortized premium

38,020

38,683

Amortized cost

679,240

690,550

Unrealized gains

Unrealized losses

(11,515)

(2,480)

Fair value

667,725

688,156

Freddie Mac [Member]

Principal Amount

397,048

403,589

Net unamortized premium

22,435

22,821

Amortized cost

419,483

426,410

Unrealized gains

Unrealized losses

(8,927)

(2,212)

Fair value

$ 410,556

$ 424,202

- Definition

Amount of debt securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 137

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 320

-Section 50

-Paragraph 2

-Subparagraph (b)-(g)

-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details