Loans and Leases (Allowance for credit losses on financing receivables) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	$ 7,141		$ 4,624
Ending Balance Under ASC 450-20	34,170		34,091
Total	41,311	37,623	38,715	40,401	41,439	36,808
Ending Balance Evaluated for Impairment Under ASC 310-10-35	81,134		83,576
Ending Balance Evaluated for Impairment Under ASC 450-20	2,823,813		2,741,594
Total	2,904,947		2,825,170
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	3,178		1,350
Ending Balance Under ASC 450-20	9,918		10,038
Total	13,096	9,436	11,388	11,268	10,287	10,547
Ending Balance Evaluated for Impairment Under ASC 310-10-35	21,696		9,031
Ending Balance Evaluated for Impairment Under ASC 450-20	733,962		703,277
Total	755,658		712,308
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	838		1,112
Ending Balance Under ASC 450-20	13,205		13,361
Total	14,043	13,671	14,473	15,300	17,057	14,621
Ending Balance Evaluated for Impairment Under ASC 310-10-35	28,018		45,583
Ending Balance Evaluated for Impairment Under ASC 450-20	1,259,319		1,243,601
Total	1,287,337		1,289,184
Agricultural and Agricultural Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	619		109
Ending Balance Under ASC 450-20	2,197		2,029
Total	2,816	3,055	2,138	2,057	2,002	1,763
Ending Balance Evaluated for Impairment Under ASC 310-10-35	19,249		16,128
Ending Balance Evaluated for Impairment Under ASC 450-20	305,090		312,183
Total	324,339		328,311
Residential Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	678		783
Ending Balance Under ASC 450-20	2,859		2,760
Total	3,537	3,580	3,543	3,868	3,899	3,001
Ending Balance Evaluated for Impairment Under ASC 310-10-35	6,986		7,443
Ending Balance Evaluated for Impairment Under ASC 450-20	262,515		242,246
Total	269,501		249,689
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	1,828		1,270
Ending Balance Under ASC 450-20	5,991		5,903
Total	7,819	7,881	7,173	7,908	8,193	6,874
Ending Balance Evaluated for Impairment Under ASC 310-10-35	5,185		5,391
Ending Balance Evaluated for Impairment Under ASC 450-20	262,927		240,287
Total	$ 268,112		$ 245,678