Allowance for Loan Losses and Credit Quality of Loans, Past Due Loans (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Aging [Abstract]
Minimum number of days past due for nonaccrual loan status	90 days
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	$ 26,700	$ 31,961
61 - 90 Days Past Due Accruing	5,842	5,894
Greater Than 90 Days Past Due Accruing	4,022	3,737
Total Past Due Accruing	36,564	41,592
Non-Accrual	50,531	49,965
Current	5,499,996	5,315,238
Ending balance of loans	5,587,091	5,406,795
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	24,292	28,124
61 - 90 Days Past Due Accruing	5,275	5,660
Greater Than 90 Days Past Due Accruing	3,931	3,657
Total Past Due Accruing	33,498	37,441
Non-Accrual	35,863	33,883
Current	4,719,539	4,405,079
Ending balance of loans	4,788,900	4,476,403
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	2,408	3,837
61 - 90 Days Past Due Accruing	567	234
Greater Than 90 Days Past Due Accruing	91	80
Total Past Due Accruing	3,066	4,151
Non-Accrual	14,668	16,082
Current	780,457	910,159
Ending balance of loans	798,191	930,392
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Ending balance of loans	2,457,906	2,392,621
Commercial Loans [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	2,244	3,368
61 - 90 Days Past Due Accruing	904	390
Greater Than 90 Days Past Due Accruing	0	105
Total Past Due Accruing	3,148	3,863
Non-Accrual	19,017	19,300
Current	2,078,328	1,967,069
Ending balance of loans	2,100,493	1,990,232
Commercial Loans [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	202	344
61 - 90 Days Past Due Accruing	0	2
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	202	346
Non-Accrual	10,046	11,498
Current	347,165	390,545
Ending balance of loans	357,413	402,389
Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	670	105
61 - 90 Days Past Due Accruing	270	247
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	940	352
Non-Accrual	2,890	3,669
Current	618,680	612,402
Ending balance of loans	622,510	616,423
Commercial [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	0	24
61 - 90 Days Past Due Accruing	0	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	0	24
Non-Accrual	6,046	6,599
Current	83,543	96,603
Ending balance of loans	89,589	103,226
Commercial Real Estate [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	104	1,366
61 - 90 Days Past Due Accruing	561	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	665	1,366
Non-Accrual	6,565	7,834
Current	1,013,177	925,116
Ending balance of loans	1,020,407	934,316
Commercial Real Estate [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	0	0
61 - 90 Days Past Due Accruing	0	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	0	0
Non-Accrual	3,369	3,559
Current	203,288	225,455
Ending balance of loans	206,657	229,014
Agricultural [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	55	150
61 - 90 Days Past Due Accruing	20	21
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	75	171
Non-Accrual	993	1,135
Current	33,292	63,856
Ending balance of loans	34,360	65,162
Agricultural Real Estate [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	0	519
61 - 90 Days Past Due Accruing	0	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	0	519
Non-Accrual	963	961
Current	25,360	35,172
Ending balance of loans	26,323	36,652
Business Banking [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,415	1,228
61 - 90 Days Past Due Accruing	53	122
Greater Than 90 Days Past Due Accruing	0	105
Total Past Due Accruing	1,468	1,455
Non-Accrual	7,606	5,701
Current	387,819	330,523
Ending balance of loans	396,893	337,679
Business Banking [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	202	320
61 - 90 Days Past Due Accruing	0	2
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	202	322
Non-Accrual	631	1,340
Current	60,334	68,487
Ending balance of loans	61,167	70,149
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Ending balance of loans	2,029,046	1,972,537
Consumer Loans [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	19,105	20,805
61 - 90 Days Past Due Accruing	4,199	4,891
Greater Than 90 Days Past Due Accruing	2,527	2,744
Total Past Due Accruing	25,831	28,440
Non-Accrual	8,458	7,478
Current	1,831,738	1,717,032
Ending balance of loans	1,866,027	1,752,950
Consumer Loans [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	667	1,768
61 - 90 Days Past Due Accruing	122	232
Greater Than 90 Days Past Due Accruing	91	80
Total Past Due Accruing	880	2,080
Non-Accrual	822	712
Current	161,317	216,795
Ending balance of loans	163,019	219,587
Indirect [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	14,686	14,093
61 - 90 Days Past Due Accruing	2,560	2,878
Greater Than 90 Days Past Due Accruing	1,785	1,583
Total Past Due Accruing	19,031	18,554
Non-Accrual	1,606	1,461
Current	1,287,966	1,141,829
Ending balance of loans	1,308,603	1,161,844
Indirect [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	451	939
61 - 90 Days Past Due Accruing	60	113
Greater Than 90 Days Past Due Accruing	82	71
Total Past Due Accruing	593	1,123
Non-Accrual	125	93
Current	77,090	123,870
Ending balance of loans	77,808	125,086
Home Equity Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	3,955	6,033
61 - 90 Days Past Due Accruing	1,528	1,888
Greater Than 90 Days Past Due Accruing	686	1,115
Total Past Due Accruing	6,169	9,036
Non-Accrual	6,748	5,931
Current	488,674	517,856
Ending balance of loans	501,591	532,823
Home Equity Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	185	753
61 - 90 Days Past Due Accruing	61	63
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	246	816
Non-Accrual	663	570
Current	78,627	85,690
Ending balance of loans	79,536	87,076
Direct [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	464	679
61 - 90 Days Past Due Accruing	111	125
Greater Than 90 Days Past Due Accruing	56	46
Total Past Due Accruing	631	850
Non-Accrual	104	86
Current	55,098	57,347
Ending balance of loans	55,833	58,283
Direct [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	31	76
61 - 90 Days Past Due Accruing	1	56
Greater Than 90 Days Past Due Accruing	9	9
Total Past Due Accruing	41	141
Non-Accrual	34	49
Current	5,600	7,235
Ending balance of loans	5,675	7,425
Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Ending balance of loans	1,100,139	1,041,637
Residential Real Estate Mortgages [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	2,943	3,951
61 - 90 Days Past Due Accruing	172	379
Greater Than 90 Days Past Due Accruing	1,404	808
Total Past Due Accruing	4,519	5,138
Non-Accrual	8,388	7,105
Current	809,473	720,978
Ending balance of loans	822,380	733,221
Residential Real Estate Mortgages [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,539	1,725
61 - 90 Days Past Due Accruing	445	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	1,984	1,725
Non-Accrual	3,800	3,872
Current	271,975	302,819
Ending balance of loans	$ 277,759	$ 308,416