Loans and Allowance for Loan Losses (Details 6) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Activity in ALLL by class of loans
Beginning balance	$ 37,633	$ 36,136	$ 37,656	$ 35,745
Charge-offs	(512)	(1,174)	(1,063)	(1,735)
Recoveries	86	117	422	281
Net charge-offs	(445)	(1,057)	(641)	(1,454)
Provisions charged to operations	248	2,013	421	2,801
Ending balance	37,436	37,092	37,436	37,092
Individually evaluated for impairment	7,680	8,611	7,680	8,611
Collectively evaluated for impairment	29,756	28,481	29,756	28,481
Allowance for credit losses: Balance at end of period	37,436	37,092	37,436	37,092
Individually evaluated for impairment	69,929	76,500	69,929	76,500
Collectively evaluated for impairment	2,983,606	2,775,581	2,983,606	2,775,581
Loans acquired with deteriorated credit quality	11,904	9,763	11,904	9,763
Ending balance	3,065,439	2,861,844	3,065,439	2,861,844	3,013,498
Non-residential real estate [Member]
Activity in ALLL by class of loans
Beginning balance	14,109	12,979	13,948	13,142
Charge-offs	(7)	(136)	(128)	(269)
Recoveries	(6)	7	31	16
Net charge-offs	(13)	(129)	(97)	(253)
Provisions charged to operations	(253)	801	498	762
Ending balance	14,349	13,651	14,349	13,651
Individually evaluated for impairment	2,986	3,694	2,986	3,694
Collectively evaluated for impairment	11,363	9,957	11,363	9,957
Allowance for credit losses: Balance at end of period	14,349	13,651	14,349	13,651
Individually evaluated for impairment	38,278	42,486	38,278	42,486
Collectively evaluated for impairment	1,102,773	938,216	1,102,773	938,216
Ending balance	1,141,051	980,702	1,141,051	980,702
Residential real estate [Member]
Activity in ALLL by class of loans
Beginning balance	9,762	9,612	9,764	8,957
Charge-offs	(95)	(312)	(131)	(501)
Recoveries	13	39	109	95
Net charge-offs	(82)	(273)	(22)	(406)
Provisions charged to operations	326	41	264	829
Ending balance	10,006	9,380	10,006	9,380
Individually evaluated for impairment	2,760	2,314	2,760	2,314
Collectively evaluated for impairment	7,246	7,066	7,246	7,066
Allowance for credit losses: Balance at end of period	10,006	9,380	10,006	9,380
Individually evaluated for impairment	20,710	19,049	20,710	19,049
Collectively evaluated for impairment	700,439	670,120	700,439	670,120
Ending balance	721,149	689,169	721,149	689,169
Non-consumer non-real estate [Member]
Activity in ALLL by class of loans
Beginning balance	9,198	9,165	9,156	9,587
Charge-offs	(313)	(179)	(330)	(184)
Recoveries	26	29	124	84
Net charge-offs	(287)	(150)	(206)	(100)
Provisions charged to operations	(353)	319	(392)	(153)
Ending balance	8,558	9,334	8,558	9,334
Individually evaluated for impairment	1,436	2,021	1,436	2,021
Collectively evaluated for impairment	7,122	7,313	7,122	7,313
Allowance for credit losses: Balance at end of period	8,558	9,334	8,558	9,334
Individually evaluated for impairment	8,377	12,085	8,377	12,085
Collectively evaluated for impairment	689,039	700,353	689,039	700,353
Ending balance	697,416	712,438	697,416	712,438
Consumer non-real estate [Member]
Activity in ALLL by class of loans
Beginning balance	2,283	2,258	2,315	2,301
Charge-offs	(77)	(223)	(191)	(328)
Recoveries	32	36	116	68
Net charge-offs	(45)	(187)	(75)	(260)
Provisions charged to operations	44	166	42	196
Ending balance	2,282	2,237	2,282	2,237
Individually evaluated for impairment	302	297	302	297
Collectively evaluated for impairment	1,980	1,940	1,980	1,940
Allowance for credit losses: Balance at end of period	2,282	2,237	2,282	2,237
Individually evaluated for impairment	2,455	2,467	2,455	2,467
Collectively evaluated for impairment	197,972	196,111	197,972	196,111
Ending balance	200,427	198,578	200,427	198,578
Other loans [Member]
Activity in ALLL by class of loans
Beginning balance	1,850	1,699	1,886	1,758
Charge-offs	(27)	(22)	(207)	(122)
Recoveries	12	5	31	7
Net charge-offs	(15)	(17)	(176)	(115)
Provisions charged to operations	19	30	144	69
Ending balance	1,854	1,712	1,854	1,712
Individually evaluated for impairment	196	285	196	285
Collectively evaluated for impairment	1,658	1,427	1,658	1,427
Allowance for credit losses: Balance at end of period	1,854	1,712	1,854	1,712
Individually evaluated for impairment	109	413	109	413
Collectively evaluated for impairment	155,875	159,824	155,875	159,824
Ending balance	155,984	160,237	155,984	160,237
Acquired loans [Member]
Activity in ALLL by class of loans
Beginning balance	431	423	587
Charge-offs	(12)	(302)	(76)	(331)
Recoveries	9	1	11	11
Net charge-offs	(3)	(301)	(65)	(320)
Provisions charged to operations	(41)	656	(135)	1,098
Ending balance	387	778	387	778
Collectively evaluated for impairment	387	778	387	778
Allowance for credit losses: Balance at end of period	387	778	387	778
Individually evaluated for impairment
Collectively evaluated for impairment	137,508	110,957	137,508	110,957
Loans acquired with deteriorated credit quality	11,904	9,763	11,904	9,763
Ending balance	$ 149,412	$ 120,720	$ 149,412	$ 120,720