Note 6 - Debt and Equity Securities - Amortized Cost and Fair Value of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Securities held-to-maturity	$ 30,886	$ 37,735
Securities held-to-maturity, fair value	29,699	35,408
Securities held-to-maturity, gross unrealized gains
Securities held-to-maturity, gross unrealized losses	1,187	2,327
Securities available for sale, amortized cost	748,350	868,009
Securities available for sale	738,354	861,381
Securities available for sale, gross unrealized gains	2,587	5,091
Securities available for sale, gross unrealized losses	12,583	11,719
Corporate Debt Securities [Member]
Securities available for sale, amortized cost	110,000	110,000
Securities available for sale	102,767	102,910
Securities available for sale, gross unrealized gains
Securities available for sale, gross unrealized losses	7,233	7,090
Municipal Debt Securities [Member]
Securities held-to-maturity	22,913	37,735
Securities held-to-maturity, fair value	21,889	35,408
Securities held-to-maturity, gross unrealized gains
Securities held-to-maturity, gross unrealized losses	1,024	2,327
Securities available for sale, amortized cost	101,680	124,984
Securities available for sale	103,199	126,903
Securities available for sale, gross unrealized gains	1,519	1,983
Securities available for sale, gross unrealized losses		64
Other Debt Obligations [Member]
Securities held-to-maturity	22,913	37,735
Securities held-to-maturity, fair value	21,889	35,408
Securities held-to-maturity, gross unrealized gains
Securities held-to-maturity, gross unrealized losses	1,024
Securities available for sale	228,704	344,905
Mutual Fund Debt Securities [Member]
Securities available for sale, amortized cost	11,575	21,366
Securities available for sale	11,575	21,366
Securities available for sale, gross unrealized gains
Securities available for sale, gross unrealized losses
FNMA [Member]
Securities held-to-maturity	7,973
Securities held-to-maturity, fair value	7,810
Securities held-to-maturity, gross unrealized gains
Securities held-to-maturity, gross unrealized losses	163
Securities available for sale, amortized cost	136,198	109,493
Securities available for sale	135,474	108,351
Securities available for sale, gross unrealized gains	330	463
Securities available for sale, gross unrealized losses	1,054	1,605
Collateralized Debt Obligations [Member]
Securities available for sale, amortized cost	10,000	85,470
Securities available for sale	10,053	86,365
Securities available for sale, gross unrealized gains	53	895
Securities available for sale, gross unrealized losses
Collateralized Mortgage Backed Securities [Member]
Securities held-to-maturity	7,973
Securities held-to-maturity, fair value	7,810
Securities held-to-maturity, gross unrealized gains
Securities held-to-maturity, gross unrealized losses	163
Securities available for sale, amortized cost	513,985	518,826
Securities available for sale	509,650	516,476
Securities available for sale, gross unrealized gains	1,015	2,213
Securities available for sale, gross unrealized losses	5,350	4,563
Other Securities [Member]
Securities available for sale, amortized cost	1,110	7,363
Securities available for sale	1,110	7,361
Securities available for sale, gross unrealized gains
Securities available for sale, gross unrealized losses		2
Available for Sale Securities Excluding Mortgage Backed Securities [Member]
Securities available for sale, amortized cost	234,365	349,183
Securities available for sale	228,704	344,905
Securities available for sale, gross unrealized gains	1,572	2,878
Securities available for sale, gross unrealized losses	7,233	7,156
REMIC and CMO [Member]
Securities available for sale, amortized cost	328,668	402,636
Securities available for sale	325,302	401,370
Securities available for sale, gross unrealized gains	595	1,607
Securities available for sale, gross unrealized losses	3,961	2,873
GNMA [Member]
Securities available for sale, amortized cost	1,016	1,319
Securities available for sale	1,088	1,427
Securities available for sale, gross unrealized gains	72	108
Securities available for sale, gross unrealized losses
FHLMC [Member]
Securities available for sale, amortized cost	48,103	5,378
Securities available for sale	47,786	5,328
Securities available for sale, gross unrealized gains	18	35
Securities available for sale, gross unrealized losses	$ 335	$ 85

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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