Loans and Leases (Allowance for credit losses on financing reveivables) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	$ 4,492	$ 4,624
Ending Balance Under ASC 450-20	33,036	34,091
Total	37,528	38,715	39,362	36,808
Ending Balance Evaluated for Impairment Under ASC 310-10-35	71,233	83,576
Ending Balance Evaluated for Impairment Under ASC 450-20	2,721,640	2,741,594
Total	2,792,873	2,825,170
Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	1,990,818	2,001,492
Agricultural Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	176	109
Ending Balance Under ASC 450-20	2,019	2,029
Total	2,195	2,138	1,847	1,763
Ending Balance Evaluated for Impairment Under ASC 310-10-35	13,222	16,128
Ending Balance Evaluated for Impairment Under ASC 450-20	301,384	312,183
Total	314,606	328,311
Residential Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	796	783
Ending Balance Under ASC 450-20	2,470	2,760
Total	3,266	3,543	3,540	3,001
Ending Balance Evaluated for Impairment Under ASC 310-10-35	7,305	7,443
Ending Balance Evaluated for Impairment Under ASC 450-20	233,148	242,246
Total	240,453	249,689
Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	1,530	1,270
Ending Balance Under ASC 450-20	6,048	5,903
Total	7,578	7,173	7,555	6,874
Ending Balance Evaluated for Impairment Under ASC 310-10-35	5,055	5,391
Ending Balance Evaluated for Impairment Under ASC 450-20	241,941	240,287
Total	246,996	245,678
Commercial | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	1,026	1,350
Ending Balance Under ASC 450-20	8,273	10,038
Total	9,299	11,388	11,019	10,547
Ending Balance Evaluated for Impairment Under ASC 310-10-35	8,457	9,031
Ending Balance Evaluated for Impairment Under ASC 450-20	684,778	703,277
Total	693,235	712,308
Commercial Real Estate | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	964	1,112
Ending Balance Under ASC 450-20	14,226	13,361
Total	15,190	14,473	15,400	14,621
Ending Balance Evaluated for Impairment Under ASC 310-10-35	37,194	45,583
Ending Balance Evaluated for Impairment Under ASC 450-20	1,260,389	1,243,601
Total	$ 1,297,583	$ 1,289,184