Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Condensed Consolidated Statements of Cash Flows [Abstract]
NET CASH PROVIDED BY OPERATING ACTIVITIES	$ 32,943	$ 36,638
INVESTING ACTIVITIES
Proceeds from maturities and calls of securities held to maturity	569	2,533
Proceeds from sales of securities available for sale	1,969	11,727
Proceeds from maturities and calls of securities available for sale	390,665	209,786
Purchases of securities available for sale	(362,134)	(237,827)
Purchases of bank premises and equipment	(1,110)	(1,804)
Proceeds from sales and redemptions of other investment securities	1,448	1,719
Net change in loans	32,595	32,872
NET CASH PROVIDED BY INVESTING ACTIVITIES	64,002	19,006
FINANCING ACTIVITIES
Cash dividends paid	(15,569)	(13,087)
Excess tax benefits from stock-based compensation arrangements	28	125
Acquisition of treasury stock	(4)	(4)
Proceeds from exercise of stock options	85	311
Distribution of treasury stock for deferred compensation plan	86	0
Repayment of long-term Federal Home Loan Bank borrowings	(97)	(50,091)
Changes in:
Deposits	63,787	(1,611)
Federal funds purchased, securities sold under agreements to repurchase and other short-term borrowings	8,567	78,095
NET CASH PROVIDED BY FINANCING ACTIVITIES	56,883	13,738
Increase in cash and cash equivalents	153,828	69,382
Cash and cash equivalents at beginning of year	636,003	461,389
Cash and cash equivalents at end of period	$ 789,831	$ 530,771