Loans and Leases (Loans and leases not covered by share agreements (past due financing receivables)) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 15,119	$ 6,306
60-89 Days Past Due	2,676	2,020
90 Days or More Past Due	9	0
Total Past Due	17,804	8,326
Current	4,200,139	3,844,467
Nonaccrual	27,023	25,070
Total	4,244,966us-gaap_NotesReceivableGross	3,877,863us-gaap_NotesReceivableGross
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,485	980
60-89 Days Past Due	729	48
90 Days or More Past Due	0	0
Total Past Due	2,214	1,028
Current	1,131,303	1,032,707
Nonaccrual	1,097	2,345
Total	1,134,614	1,036,080
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	9,336	1,788
60-89 Days Past Due	1,177	111
90 Days or More Past Due	0	0
Total Past Due	10,513	1,899
Current	1,907,619	1,693,554
Nonaccrual	14,569	11,607
Total	1,932,701	1,707,060
Commercial and commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	10,821	2,768
60-89 Days Past Due	1,906	159
90 Days or More Past Due	0	0
Total Past Due	12,727	2,927
Current	3,038,922	2,726,261
Nonaccrual	15,666	13,952
Total	3,067,315	2,743,140
Agricultural and agricultural real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	569	119
60-89 Days Past Due	129	50
90 Days or More Past Due	9	0
Total Past Due	707	169
Current	409,658	422,219
Nonaccrual	1,367	1,439
Total	411,732	423,827
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,483	1,037
60-89 Days Past Due	139	445
90 Days or More Past Due	0	0
Total Past Due	1,622	1,482
Current	404,861	371,982
Nonaccrual	7,455	6,877
Total	413,938	380,341
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	2,246	2,382
60-89 Days Past Due	502	1,366
90 Days or More Past Due	0	0
Total Past Due	2,748	3,748
Current	346,698	324,005
Nonaccrual	2,535	2,802
Total	$ 351,981	$ 330,555

Financing receivables that are less than 60 days past due but more than 29 days past due.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7A

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953401-111524

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Financing receivables that are less than 90 days past due but more than 59 days past due.

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Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5111-111524

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Financing receivables that are current.

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Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.10(3))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 10

-Subparagraph 3

-Article 9

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