Allowance for Loan Losses and Credit Quality of Loans, Past Due Loans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 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	$ 22,234	$ 27,402
61 - 90 Days Past Due Accruing	5,475	6,150
Greater Than 90 Days Past Due Accruing	2,601	4,941
Total Past Due Accruing	30,310	38,493
Non-Accrual	45,053	41,074
Current	5,547,660	5,515,704
Ending balance of loans	5,623,023	5,595,271
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Ending balance of loans	2,484,300	2,473,702
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Ending balance of loans	2,013,123	2,005,980
Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Ending balance of loans	1,125,600	1,115,589
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	20,089	25,496
61 - 90 Days Past Due Accruing	4,725	5,805
Greater Than 90 Days Past Due Accruing	2,560	4,204
Total Past Due Accruing	27,374	35,505
Non-Accrual	31,099	30,845
Current	4,845,780	4,781,587
Ending balance of loans	4,904,253	4,847,937
Originated Loans [Member] \| Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,219	1,010
61 - 90 Days Past Due Accruing	229	970
Greater Than 90 Days Past Due Accruing	77	84
Total Past Due Accruing	1,525	2,064
Non-Accrual	15,235	13,431
Current	2,142,302	2,124,876
Ending balance of loans	2,159,062	2,140,371
Originated Loans [Member] \| Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	348	0
61 - 90 Days Past Due Accruing	0	735
Greater Than 90 Days Past Due Accruing	35	0
Total Past Due Accruing	383	735
Non-Accrual	1,019	1,012
Current	620,111	613,400
Ending balance of loans	621,513	615,147
Originated Loans [Member] \| Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	133	192
61 - 90 Days Past Due Accruing	37	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	170	192
Non-Accrual	6,231	4,127
Current	1,076,218	1,064,549
Ending balance of loans	1,082,619	1,068,868
Originated Loans [Member] \| Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	129	0
61 - 90 Days Past Due Accruing	0	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	129	0
Non-Accrual	800	817
Current	31,080	32,130
Ending balance of loans	32,009	32,947
Originated Loans [Member] \| Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	7	19
61 - 90 Days Past Due Accruing	0	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	7	19
Non-Accrual	561	565
Current	23,963	24,390
Ending balance of loans	24,531	24,974
Originated Loans [Member] \| Business Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	602	799
61 - 90 Days Past Due Accruing	192	235
Greater Than 90 Days Past Due Accruing	42	84
Total Past Due Accruing	836	1,118
Non-Accrual	6,624	6,910
Current	390,930	390,407
Ending balance of loans	398,390	398,435
Originated Loans [Member] \| Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	15,676	21,585
61 - 90 Days Past Due Accruing	3,232	4,739
Greater Than 90 Days Past Due Accruing	2,228	2,864
Total Past Due Accruing	21,136	29,188
Non-Accrual	8,346	8,644
Current	1,850,966	1,820,892
Ending balance of loans	1,880,448	1,858,724
Originated Loans [Member] \| Indirect [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	11,794	16,434
61 - 90 Days Past Due Accruing	2,348	3,154
Greater Than 90 Days Past Due Accruing	1,722	1,991
Total Past Due Accruing	15,864	21,579
Non-Accrual	2,056	1,964
Current	1,327,653	1,286,507
Ending balance of loans	1,345,573	1,310,050
Originated Loans [Member] \| Home Equity Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	3,507	4,591
61 - 90 Days Past Due Accruing	804	1,428
Greater Than 90 Days Past Due Accruing	484	821
Total Past Due Accruing	4,795	6,840
Non-Accrual	6,160	6,596
Current	470,340	479,444
Ending balance of loans	481,295	492,880
Originated Loans [Member] \| Direct [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	375	560
61 - 90 Days Past Due Accruing	80	157
Greater Than 90 Days Past Due Accruing	22	52
Total Past Due Accruing	477	769
Non-Accrual	130	84
Current	52,973	54,941
Ending balance of loans	53,580	55,794
Originated Loans [Member] \| Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	3,194	2,901
61 - 90 Days Past Due Accruing	1,264	96
Greater Than 90 Days Past Due Accruing	255	1,256
Total Past Due Accruing	4,713	4,253
Non-Accrual	7,518	8,770
Current	852,512	835,819
Ending balance of loans	864,743	848,842
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	2,145	1,906
61 - 90 Days Past Due Accruing	750	345
Greater Than 90 Days Past Due Accruing	41	737
Total Past Due Accruing	2,936	2,988
Non-Accrual	13,954	10,229
Current	701,880	734,117
Ending balance of loans	718,770	747,334
Acquired Loans [Member] \| Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	42	5
61 - 90 Days Past Due Accruing	2	15
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	44	20
Non-Accrual	10,252	6,340
Current	314,942	326,971
Ending balance of loans	325,238	333,331
Acquired Loans [Member] \| Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	42	0
61 - 90 Days Past Due Accruing	0	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	42	0
Non-Accrual	2,517	3,009
Current	70,010	72,255
Ending balance of loans	72,569	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	7,247	2,666
Current	190,518	197,222
Ending balance of loans	197,765	199,888
Acquired Loans [Member] \| Business Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	0	5
61 - 90 Days Past Due Accruing	2	15
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	2	20
Non-Accrual	488	665
Current	54,414	57,494
Ending balance of loans	54,904	58,179
Acquired Loans [Member] \| Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	631	739
61 - 90 Days Past Due Accruing	98	65
Greater Than 90 Days Past Due Accruing	41	66
Total Past Due Accruing	770	870
Non-Accrual	601	696
Current	131,304	145,690
Ending balance of loans	132,675	147,256
Acquired Loans [Member] \| Indirect [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	343	518
61 - 90 Days Past Due Accruing	44	5
Greater Than 90 Days Past Due Accruing	37	54
Total Past Due Accruing	424	577
Non-Accrual	146	106
Current	53,577	64,540
Ending balance of loans	54,147	65,223
Acquired Loans [Member] \| Home Equity Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	212	190
61 - 90 Days Past Due Accruing	50	60
Greater Than 90 Days Past Due Accruing	0	5
Total Past Due Accruing	262	255
Non-Accrual	427	557
Current	73,029	75,904
Ending balance of loans	73,718	76,716
Acquired Loans [Member] \| Direct [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	76	31
61 - 90 Days Past Due Accruing	4	0
Greater Than 90 Days Past Due Accruing	4	7
Total Past Due Accruing	84	38
Non-Accrual	28	33
Current	4,698	5,246
Ending balance of loans	4,810	5,317
Acquired Loans [Member] \| Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,472	1,162
61 - 90 Days Past Due Accruing	650	265
Greater Than 90 Days Past Due Accruing	0	671
Total Past Due Accruing	2,122	2,098
Non-Accrual	3,101	3,193
Current	255,634	261,456
Ending balance of loans	$ 260,857	$ 266,747

Allowance for Loan Losses and Credit Quality of Loans, Past Due Loans (Details) (USD $)
In Thousands, unless otherwise specified

3 Months Ended

Mar. 31, 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

$ 22,234

$ 27,402

61 - 90 Days Past Due Accruing