Note 13 - Condensed Financial Statements of Parent Company (Details) - Condensed Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash Flows from Operating Expenses
Net income	$ 16,914	$ 17,790	$ 17,747
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of premiums and accretion of discounts, net	138	171	224
Depreciation expense	732	726	764
(Gains) Losses on disposal of fixed assets	94	(11)	(3)
Net change in other assets	(574)	1,760	(8)
Net change in other liabilities	(428)	83	(175)
Losses on securities	(2)	46	(60)
Cash Flows from Investing Activities
Net Change in interest-bearing deposits	(4,482)	(781)	1,634
Purchases of securities available for sale	(33,905)	(83,996)	(171,577)
Purchases of securities held to maturity	(6,381)	(13,484)	(47,803)
Maturities and calls of securities available for sale	11,088	63,886	151,175
Proceeds from sale of premises and equipment	453	11
Cash Flows from Financing Activities
Cash dividends paid	(7,853)	(7,781)	(7,639)
Exercise of stock options	58		119
Net change in cash	(389)	(1,500)	2,886
Parent Company [Member]
Cash Flows from Operating Expenses
Net income	16,914	17,790	17,747
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed net income of subsidiaries	(9,718)	(10,545)	(10,512)
Amortization of premiums and accretion of discounts, net	1		1
Depreciation expense	9	17	12
(Gains) Losses on disposal of fixed assets	94
Net change in refundable income taxes due from subsidiaries	96	77	77
Net change in other assets	(63)	3	(199)
Net change in other liabilities	(33)	20	(124)
Losses on securities		94
Net cash provided by operating activities	7,300	7,456	7,002
Cash Flows from Investing Activities
Net Change in interest-bearing deposits	213	(2)	(124)
Purchases of securities available for sale		(612)	(691)
Purchases of securities held to maturity	(453)
Maturities and calls of securities available for sale	455	945	1,352
Proceeds from sale of premises and equipment	263
Net cash provided by investing activities	478	331	537
Cash Flows from Financing Activities
Cash dividends paid	(7,853)	(7,781)	(7,639)
Exercise of stock options	58		119
Net cash used in financing activities	(7,795)	(7,781)	(7,520)
Net change in cash	17	6	19
Cash due from subsidiaries at beginning of year	27	21	2
Cash due from subsidiaries at end of year	$ 10	$ 27	$ 21