Loans and Leases (Allowance for credit losses on financing receivables) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	$ 1,934	$ 2,697
Ending Balance Under ASC 450-20	39,920	38,752
Total	41,854	41,449	38,573	41,685
Ending Balance Evaluated for Impairment Under ASC 310-10-35	59,541	61,724
Ending Balance Evaluated for Impairment Under ASC 450-20	4,185,425	3,816,139
Total	4,244,966us-gaap_NotesReceivableGross	3,877,863us-gaap_NotesReceivableGross
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	205	754
Ending Balance Under ASC 450-20	11,483	11,155
Total	11,688	11,909	11,633	13,099
Ending Balance Evaluated for Impairment Under ASC 310-10-35	3,566	4,526
Ending Balance Evaluated for Impairment Under ASC 450-20	1,131,048	1,031,554
Total	1,134,614	1,036,080
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	466	636
Ending Balance Under ASC 450-20	16,169	15,262
Total	16,635	15,898	13,010	14,152
Ending Balance Evaluated for Impairment Under ASC 310-10-35	35,872	35,771
Ending Balance Evaluated for Impairment Under ASC 450-20	1,896,829	1,671,289
Total	1,932,701	1,707,060
Agricultural and agricultural real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	49	52
Ending Balance Under ASC 450-20	3,167	3,243
Total	3,216	3,295	2,571	2,992
Ending Balance Evaluated for Impairment Under ASC 310-10-35	4,989	5,049
Ending Balance Evaluated for Impairment Under ASC 450-20	406,743	418,778
Total	411,732	423,827
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	491	442
Ending Balance Under ASC 450-20	3,254	3,299
Total	3,745	3,741	3,671	3,720
Ending Balance Evaluated for Impairment Under ASC 310-10-35	10,401	10,235
Ending Balance Evaluated for Impairment Under ASC 450-20	403,537	370,106
Total	413,938	380,341
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	723	813
Ending Balance Under ASC 450-20	5,847	5,793
Total	6,570	6,606	7,376	7,722
Ending Balance Evaluated for Impairment Under ASC 310-10-35	4,713	6,143
Ending Balance Evaluated for Impairment Under ASC 450-20	347,268	324,412
Total	$ 351,981	$ 330,555

A valuation allowance for financing receivables that are expected to be uncollectible.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

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+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

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The balance of financing receivables that were collectively evaluated for impairment.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (h)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

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The balance of financing receivables that were individually evaluated for impairment.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (h)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

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- Definition

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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