Note 4 - Debt and Equity Securities - Amortized Cost and Fair Value of Securities (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Securities held-to-maturity, amortized cost	$ 31,235,000	$ 30,886,000
Securities held-to-maturity, fair value	28,911,000	29,699,000
Securities held-to-maturity, gross unrealized gains		0
Securities held-to-maturity, gross unrealized losses	2,324,000	1,187,000
Securities available for sale, amortized cost, total other securities	748,952,000	748,350,000
Securities available for sale, fair value	729,261,000	738,354,000
Securities available for sale, gross unrealized gains	1,526,000	2,587,000
Securities available for sale, gross unrealized losses	21,217,000	12,583,000
Corporate Debt Securities [Member]
Securities available for sale, amortized cost, total other securities	110,000,000	110,000,000
Securities available for sale, fair value	101,578,000	102,767,000
Securities available for sale, gross unrealized gains
Securities available for sale, gross unrealized losses	8,422,000	7,233,000
US States and Political Subdivisions Debt Securities [Member]
Securities held-to-maturity, amortized cost	23,267,000	22,913,000
Securities held-to-maturity, fair value	21,347,000	21,889,000
Securities held-to-maturity, gross unrealized gains		0
Securities held-to-maturity, gross unrealized losses	1,920,000	1,024,000
Securities available for sale, amortized cost, total other securities	101,129,000	101,680,000
Securities available for sale, fair value	102,289,000	103,199,000
Securities available for sale, gross unrealized gains	1,191,000	1,519,000
Securities available for sale, gross unrealized losses	31,000
Other Debt Obligations [Member]
Securities held-to-maturity, amortized cost	23,267,000	22,913,000
Securities held-to-maturity, fair value	21,347,000	21,889,000
Securities held-to-maturity, gross unrealized gains
Securities held-to-maturity, gross unrealized losses	1,920,000	1,024,000
Securities available for sale, fair value	216,480,000	228,704,000
Mutual Fund Debt Securities [Member]
Securities available for sale, amortized cost, total other securities	11,451,000	11,575,000
Securities available for sale, fair value	11,451,000	11,575,000
Securities available for sale, gross unrealized gains
Securities available for sale, gross unrealized losses
FNMA [Member]
Securities held-to-maturity, amortized cost	7,968,000	7,973,000
Securities held-to-maturity, fair value	7,564,000	7,810,000
Securities held-to-maturity, gross unrealized gains
Securities held-to-maturity, gross unrealized losses	404,000	163,000
Securities available for sale, amortized cost, total other securities	131,918,000	136,198,000
Securities available for sale, fair value	128,535,000	135,474,000
Securities available for sale, gross unrealized gains	68,000	330,000
Securities available for sale, gross unrealized losses	3,451,000	1,054,000
Other Securities [Member]
Securities available for sale, amortized cost, total other securities	1,162,000	1,110,000
Securities available for sale, fair value	1,162,000	1,110,000
Securities available for sale, gross unrealized gains
Securities available for sale, gross unrealized losses
Collateralized Debt Obligations [Member]
Securities available for sale, amortized cost, total other securities		10,000,000
Securities available for sale, fair value		10,053,000
Securities available for sale, gross unrealized gains		53,000
Securities available for sale, gross unrealized losses
Collateralized Mortgage Backed Securities [Member]
Securities held-to-maturity, amortized cost	7,968,000	7,973,000
Securities held-to-maturity, fair value	7,564,000	7,810,000
Securities held-to-maturity, gross unrealized gains
Securities held-to-maturity, gross unrealized losses	404,000	163,000
Securities available for sale, amortized cost, total other securities	525,210,000	513,985,000
Securities available for sale, fair value	512,781,000	509,650,000
Securities available for sale, gross unrealized gains	335,000	1,015,000
Securities available for sale, gross unrealized losses	12,764,000	5,350,000
Available for Sale Securities Excluding Mortgage Backed Securities [Member]
Securities available for sale, amortized cost, total other securities	223,742,000	234,365,000
Securities available for sale, fair value	216,480,000	228,704,000
Securities available for sale, gross unrealized gains	1,191,000	1,572,000
Securities available for sale, gross unrealized losses	8,453,000	7,233,000
REMIC and CMO [Member]
Securities available for sale, amortized cost, total other securities	346,414,000	328,668,000
Securities available for sale, fair value	338,368,000	325,302,000
Securities available for sale, gross unrealized gains	188,000	595,000
Securities available for sale, gross unrealized losses	8,234,000	3,961,000
GNMA [Member]
Securities available for sale, amortized cost, total other securities	940,000	1,016,000
Securities available for sale, fair value	1,004,000	1,088,000
Securities available for sale, gross unrealized gains	64,000	72,000
Securities available for sale, gross unrealized losses
FHLMC [Member]
Securities available for sale, amortized cost, total other securities	45,938,000	48,103,000
Securities available for sale, fair value	44,874,000	47,786,000
Securities available for sale, gross unrealized gains	15,000	18,000
Securities available for sale, gross unrealized losses	$ 1,079,000	$ 335,000

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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