Note 7 - Investment Securities - Investment Securities (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Investment securities available for sale, amortized cost	$ 1,271,291,000	$ 1,336,345,000
Investment securities available for sale, gross unrealized gains	1,506,000	13,965,000
Investment securities available for sale, gross unrealized losses	31,692,000	16,684,000
Securities available-for-sale	1,241,105,000	1,333,626,000	$ 1,300,000,000
US Treasury Securities [Member]
Investment securities available for sale, amortized cost	124,842,000	249,877,000
Investment securities available for sale, gross unrealized gains
Investment securities available for sale, gross unrealized losses	247,000	357,000
Securities available-for-sale	124,595,000	249,520,000
US Government Corporations and Agencies Securities [Member]
Investment securities available for sale, amortized cost	8,794,000	9,047,000
Investment securities available for sale, gross unrealized gains		11,000
Investment securities available for sale, gross unrealized losses	99,000	70,000
Securities available-for-sale	8,695,000	8,988,000
US Government-sponsored Enterprises Debt Securities [Member]
Investment securities available for sale, amortized cost	400,000,000	400,000,000
Investment securities available for sale, gross unrealized gains
Investment securities available for sale, gross unrealized losses	14,080,000	9,664,000
Securities available-for-sale	385,920,000	390,336,000
US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, amortized cost	924,000	1,944,000
Investment securities available for sale, gross unrealized gains
Investment securities available for sale, gross unrealized losses	20,000	30,000
Securities available-for-sale	904,000	1,914,000
Collateralized Mortgage Backed Securities [Member]
Investment securities available for sale, amortized cost	655,327,000	577,987,000
Investment securities available for sale, gross unrealized gains	226,000	241,000
Investment securities available for sale, gross unrealized losses	17,194,000	6,259,000
Securities available-for-sale	638,359,000	571,969,000
Collateralized Mortgage Obligations [Member]
Investment securities available for sale, amortized cost	1,398,000	1,533,000
Investment securities available for sale, gross unrealized gains
Investment securities available for sale, gross unrealized losses	27,000	17,000
Securities available-for-sale	1,371,000	1,516,000
Corporate Debt Securities [Member]
Investment securities available for sale, amortized cost	80,006,000	80,007,000
Investment securities available for sale, gross unrealized gains	1,280,000	1,291,000
Investment securities available for sale, gross unrealized losses	25,000	17,000
Securities available-for-sale	$ 81,261,000	81,281,000
Mutual Funds [Member]
Investment securities available for sale, amortized cost		6,500,000
Investment securities available for sale, gross unrealized gains
Investment securities available for sale, gross unrealized losses		270,000
Securities available-for-sale		6,230,000
Preferred Stock of Government Sponsored Entities [Member]
Investment securities available for sale, amortized cost		5,842,000
Investment securities available for sale, gross unrealized gains		4,260,000
Investment securities available for sale, gross unrealized losses
Securities available-for-sale		10,102,000
Other Equity Securities [Member]
Investment securities available for sale, amortized cost		3,608,000
Investment securities available for sale, gross unrealized gains		8,162,000
Investment securities available for sale, gross unrealized losses
Securities available-for-sale		$ 11,770,000

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).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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Amount, before tax, of unrealized loss 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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