Allowance for Loan Losses and Credit Quality of Loans, Past Due Loans (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
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	$ 26,994	$ 27,402
61 - 90 Days Past Due Accruing	5,997	6,150
Greater Than 90 Days Past Due Accruing	1,994	4,941
Total Past Due Accruing	34,985	38,493
Non-Accrual	42,286	41,074
Current	5,693,617	5,515,704
Ending balance of loans	5,770,888	5,595,271
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Ending balance of loans	2,565,590	2,473,702
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Ending balance of loans	2,051,540	2,005,980
Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Ending balance of loans	1,153,758	1,115,589
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	25,411	25,496
61 - 90 Days Past Due Accruing	5,459	5,805
Greater Than 90 Days Past Due Accruing	1,858	4,204
Total Past Due Accruing	32,728	35,505
Non-Accrual	28,339	30,845
Current	5,018,336	4,781,587
Ending balance of loans	5,079,403	4,847,937
Originated Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	3,041	1,010
61 - 90 Days Past Due Accruing	179	970
Greater Than 90 Days Past Due Accruing	0	84
Total Past Due Accruing	3,220	2,064
Non-Accrual	13,915	13,431
Current	2,229,037	2,124,876
Ending balance of loans	2,246,172	2,140,371
Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	268	0
61 - 90 Days Past Due Accruing	7	735
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	275	735
Non-Accrual	22	1,012
Current	629,818	613,400
Ending balance of loans	630,115	615,147
Originated Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,274	192
61 - 90 Days Past Due Accruing	28	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	1,302	192
Non-Accrual	6,825	4,127
Current	1,148,828	1,064,549
Ending balance of loans	1,156,955	1,068,868
Originated Loans [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	3	0
61 - 90 Days Past Due Accruing	67	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	70	0
Non-Accrual	1,041	817
Current	31,704	32,130
Ending balance of loans	32,815	32,947
Originated Loans [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	18	19
61 - 90 Days Past Due Accruing	0	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	18	19
Non-Accrual	326	565
Current	26,380	24,390
Ending balance of loans	26,724	24,974
Originated Loans [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,478	799
61 - 90 Days Past Due Accruing	77	235
Greater Than 90 Days Past Due Accruing	0	84
Total Past Due Accruing	1,555	1,118
Non-Accrual	5,701	6,910
Current	392,307	390,407
Ending balance of loans	399,563	398,435
Originated Loans [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	19,501	21,585
61 - 90 Days Past Due Accruing	4,318	4,739
Greater Than 90 Days Past Due Accruing	1,684	2,864
Total Past Due Accruing	25,503	29,188
Non-Accrual	6,838	8,644
Current	1,898,883	1,820,892
Ending balance of loans	1,931,224	1,858,724
Originated Loans [Member] | Indirect [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	14,212	16,434
61 - 90 Days Past Due Accruing	3,035	3,154
Greater Than 90 Days Past Due Accruing	1,250	1,991
Total Past Due Accruing	18,497	21,579
Non-Accrual	1,553	1,964
Current	1,378,754	1,286,507
Ending balance of loans	1,398,804	1,310,050
Originated Loans [Member] | Home Equity Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	4,941	4,591
61 - 90 Days Past Due Accruing	1,172	1,428
Greater Than 90 Days Past Due Accruing	328	821
Total Past Due Accruing	6,441	6,840
Non-Accrual	5,226	6,596
Current	466,301	479,444
Ending balance of loans	477,968	492,880
Originated Loans [Member] | Direct [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	348	560
61 - 90 Days Past Due Accruing	111	157
Greater Than 90 Days Past Due Accruing	106	52
Total Past Due Accruing	565	769
Non-Accrual	59	84
Current	53,828	54,941
Ending balance of loans	54,452	55,794
Originated Loans [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	2,869	2,901
61 - 90 Days Past Due Accruing	962	96
Greater Than 90 Days Past Due Accruing	174	1,256
Total Past Due Accruing	4,005	4,253
Non-Accrual	7,586	8,770
Current	890,416	835,819
Ending balance of loans	902,007	848,842
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,583	1,906
61 - 90 Days Past Due Accruing	538	345
Greater Than 90 Days Past Due Accruing	136	737
Total Past Due Accruing	2,257	2,988
Non-Accrual	13,947	10,229
Current	675,281	734,117
Ending balance of loans	691,485	747,334
Acquired Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	181	5
61 - 90 Days Past Due Accruing	5	15
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	186	20
Non-Accrual	10,165	6,340
Current	309,067	326,971
Ending balance of loans	319,418	333,331
Acquired Loans [Member] | Commercial [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	2,509	3,009
Current	75,153	72,255
Ending balance of loans	77,662	75,264
Acquired Loans [Member] | Commercial Real Estate [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	7,204	2,666
Current	182,634	197,222
Ending balance of loans	189,838	199,888
Acquired Loans [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	181	5
61 - 90 Days Past Due Accruing	5	15
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	186	20
Non-Accrual	452	665
Current	51,280	57,494
Ending balance of loans	51,918	58,179
Acquired Loans [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	393	739
61 - 90 Days Past Due Accruing	127	65
Greater Than 90 Days Past Due Accruing	75	66
Total Past Due Accruing	595	870
Non-Accrual	716	696
Current	119,005	145,690
Ending balance of loans	120,316	147,256
Acquired Loans [Member] | Indirect [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	242	518
61 - 90 Days Past Due Accruing	32	5
Greater Than 90 Days Past Due Accruing	0	54
Total Past Due Accruing	274	577
Non-Accrual	125	106
Current	43,418	64,540
Ending balance of loans	43,817	65,223
Acquired Loans [Member] | Home Equity Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	130	190
61 - 90 Days Past Due Accruing	61	60
Greater Than 90 Days Past Due Accruing	67	5
Total Past Due Accruing	258	255
Non-Accrual	555	557
Current	71,457	75,904
Ending balance of loans	72,270	76,716
Acquired Loans [Member] | Direct [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	21	31
61 - 90 Days Past Due Accruing	34	0
Greater Than 90 Days Past Due Accruing	8	7
Total Past Due Accruing	63	38
Non-Accrual	36	33
Current	4,130	5,246
Ending balance of loans	4,229	5,317
Acquired Loans [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,009	1,162
61 - 90 Days Past Due Accruing	406	265
Greater Than 90 Days Past Due Accruing	61	671
Total Past Due Accruing	1,476	2,098
Non-Accrual	3,066	3,193
Current	247,209	261,456
Ending balance of loans	$ 251,751	$ 266,747