Note 6 - Investment Securities (Detail) - Temporarily Impaired Securities (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Dec. 31, 2012
Securities Available-for-Sale
Investment Securities - Less than 12 Months - Fair Value	$ 333,446	$ 102,668
Investment Securities - Less than 12 Months - Unrealized Losses	1,709	2,538
Investment Securities - 12 Months or longer - Fair Value	196,804	254,276
Investment Securities- 12 Months or longer - Unrealized Losses	9,064	11,612
Investment Securities - Fair Value	530,250	356,944
Investment Securities - Unrealized Losses	10,773	14,150
Collateralized Mortgage Backed Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	321,604	231
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	1,551	1
Securities Available-for-Sale - 12 Months or longer - Fair Value	163	170
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	1	1
Securities Available-for-Sale - Fair Value	321,767	401
Securities Available-for-Sale - Unrealized Losses	1,552	2
Mortgage Backed Securities Non Agency Member
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	0	0
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	0	0
Securities Available-for-Sale - 12 Months or longer - Fair Value	96	96
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	1	2
Securities Available-for-Sale - Fair Value	96	96
Securities Available-for-Sale - Unrealized Losses	1	2
Collateralized Mortgage Obligations [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	0	0
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	0	0
Securities Available-for-Sale - 12 Months or longer - Fair Value	417	439
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	54	35
Securities Available-for-Sale - Fair Value	417	439
Securities Available-for-Sale - Unrealized Losses	54	35
Asset-backed Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	0	0
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	0	0
Securities Available-for-Sale - 12 Months or longer - Fair Value	132	141
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	4	4
Securities Available-for-Sale - Fair Value	132	141
Securities Available-for-Sale - Unrealized Losses	4	4
Corporate Debt Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	9,855	52,468
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	145	2,532
Securities Available-for-Sale - 12 Months or longer - Fair Value	195,996	253,430
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	9,004	11,570
Securities Available-for-Sale - Fair Value	205,851	305,898
Securities Available-for-Sale - Unrealized Losses	9,149	14,102
Mutual Funds Member
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	1,987
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	13
Securities Available-for-Sale - 12 Months or longer - Fair Value	0
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	0
Securities Available-for-Sale - Fair Value	1,987
Securities Available-for-Sale - Unrealized Losses	13
Total [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	333,446	102,668
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	1,709	2,538
Securities Available-for-Sale - 12 Months or longer - Fair Value	196,804	254,276
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	9,064	11,612
Securities Available-for-Sale - Fair Value	530,250	356,944
Securities Available-for-Sale - Unrealized Losses	10,773	14,150
Securities Held-to-Maturity
Total securities held-to-maturity		0
Total securities held-to-maturity		0
Total securities held-to-maturity		0
Total securities held-to-maturity		0
Total securities held-to-maturity		0
Total securities held-to-maturity		0
US Treasury Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value		49,969
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses		5
Securities Available-for-Sale - 12 Months or longer - Fair Value		0
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses		0
Securities Available-for-Sale - Fair Value		49,969
Securities Available-for-Sale - Unrealized Losses		$ 5

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