Note 21 - Parent Company Only Financial Information (Detail) - Condensed Statements of Cash Flows for the Holding Company: (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating activities:
Net income	$ 34,331	$ 35,348	$ 38,835
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income tax provision	(804)	685	(8,041)
Fair value adjustments for financial assets and financial liabilities	(55)	(1,960)	(47)
Stock based compensation expense	3,260	2,686	2,249
Net cash provided by operating activities	71,097	64,720	67,187
Investing activities:
Purchases of securities available for sale	(311,654)	(157,741)	(397,909)
Proceeds from sales and calls of securities available for sale	12,637	8,000	91,788
Net cash provided by (used in) investing activities	(197,988)	22,693	(180,919)
Financing activities:
Purchase of treasury stock	(5,551)	(7,722)	(347)
Cash dividends paid	(15,817)	(15,910)	(15,788)
Stock options exercised	885	2,040	458
Net cash used in financing activities	111,595	(79,481)	133,095
Net (decrease) increase in cash and cash equivalents	(15,296)	7,932	19,363
Cash and cash equivalents, beginning of year	55,721	47,789	28,426
Cash and cash equivalents, end of year	40,425	55,721	47,789
Holding Company [Member]
Operating activities:
Net income	34,331	35,348	38,835
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of the Bank	(14,835)	(14,526)	(29,921)
Deferred income tax provision	858	3,003	972
Fair value adjustments for financial assets and financial liabilities	(1,991)	(5,725)	(2,253)
Stock based compensation expense	3,105	2,720	2,154
Net change in operating assets and liabilities	1,287	1,542	1,499
Net cash provided by operating activities	22,755	22,361	11,286
Investing activities:
Purchases of securities available for sale	(29)	(37)	(62)
Proceeds from sales and calls of securities available for sale			750
Net cash provided by (used in) investing activities	(29)	(37)	688
Financing activities:
Purchase of treasury stock	(5,622)	(7,722)	(347)
Cash dividends paid	(15,817)	(15,910)	(15,788)
Stock options exercised	956	2,040	458
Net cash used in financing activities	(20,483)	(21,592)	(15,677)
Net (decrease) increase in cash and cash equivalents	2,243	732	(3,703)
Cash and cash equivalents, beginning of year	18,798	18,066	21,769
Cash and cash equivalents, end of year	$ 21,041	$ 18,798	$ 18,066