Parent Company Only Financial Information (Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended	3 Months Ended								12 Months Ended
	Sep. 28, 2011	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income		$ 9,407	$ 13,587	$ 13,957	$ 12,841	$ 6,248	$ 7,338	$ 10,221	$ 4,237	$ 49,792	$ 28,044	$ 23,903
Securities gains, net										(13,998)	(13,104)	(6,834)
(Increase) decrease in trading account securities										(47)	(89)	451
Other, net										5,263	5,039	5,856
NET CASH PROVIDED BY OPERATING ACTIVITIES										48,698	58,484	92,149
Cash flows from investing activities:
Purchases of available for sale securities										(1,077,813)	(788,543)	(715,164)
Proceeds from the maturity of and principal paydowns on securities available for sale										288,774	295,137	252,514
Proceeds from sales of available for sale securities										580,775	493,167	399,901
NET CASH PROVIDED (USED) BY INVESTING ACTIVITIES										(349,713)	(199,972)	(170,829)
Cash flows from financing activities:
Net change in short-term borrowings										(45,455)	34,217	73,515
Proceeds from other borrowings										11,700	18,565	25,075
Repayments of other borrowings										(6,806)	(8,272)	(113,977)
Proceeds from issuance of preferred stock										0	81,698	0
Payment for the repurchase of preferred stock										0	(81,698)	0
Redemption of warrant	(1,800)									0	(1,800)	0
Cash dividends paid										(11,695)	(11,172)	(10,606)
Purchase of treasury stock										(2,937)	(389)	(212)
Proceeds from issuance of common stock										9,557	1,428	1,360
NET CASH PROVIDED (USED) BY FINANCING ACTIVITIES										339,235	208,750	(41,158)
Net increase (decrease) in cash and cash equivalents										38,220	67,262	(119,838)
Cash and cash equivalents at beginning of year					129,834				62,572	129,834	62,572	182,410
CASH AND CASH EQUIVALENTS AT END OF PERIOD		168,054				129,834				168,054	129,834	62,572
Parent
Cash flows from operating activities:
Net income										49,792	28,044	23,903
Undistributed earnings of subsidiaries										(19,739)	(12,852)	(12,605)
Securities gains, net										0	(1,424)	(101)
(Increase) decrease in due from subsidiaries										(4,250)	0	2,000
Increase in accrued expenses and other liabilities										4,448	5,714	897
(Increase) in other assets										(7,163)	(2,157)	(5,443)
(Increase) decrease in trading account securities										(47)	(89)	451
Other, net										1,776	(442)	(2,354)
NET CASH PROVIDED BY OPERATING ACTIVITIES										24,817	16,794	6,748
Cash flows from investing activities:
Capital contributions to subsidiaries										(32,841)	(6,000)	(21,047)
Purchases of available for sale securities										(195)	0	(8,101)
Proceeds from the maturity of and principal paydowns on securities available for sale										0	0	1,644
Proceeds from sales of available for sale securities										0	1,507	16,814
Proceeds from retirement of debt										155	0	0
NET CASH PROVIDED (USED) BY INVESTING ACTIVITIES										(32,881)	(4,493)	(10,690)
Cash flows from financing activities:
Net change in short-term borrowings										0	(5,000)	0
Proceeds from other borrowings										10,000	18,165	24,844
Repayments of other borrowings										(6,374)	(3,938)	(240)
Proceeds from issuance of preferred stock										0	81,698	0
Payment for the repurchase of preferred stock										0	(81,698)	0
Redemption of warrant										0	(1,800)	0
Cash dividends paid										(11,695)	(11,172)	(10,606)
Purchase of treasury stock										(2,937)	(389)	(212)
Proceeds from issuance of common stock										9,557	1,428	1,360
NET CASH PROVIDED (USED) BY FINANCING ACTIVITIES										(1,449)	(2,706)	15,146
Net increase (decrease) in cash and cash equivalents										(9,513)	9,595	11,204
Cash and cash equivalents at beginning of year					26,960				17,365	26,960	17,365	6,161
CASH AND CASH EQUIVALENTS AT END OF PERIOD		$ 17,447				$ 26,960				$ 17,447	$ 26,960	$ 17,365