Loans and Leases (Allowance for credit losses on financing receivables) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	$ 2,502		$ 2,697
Ending Balance Under ASC 450-20	44,603		38,752
Total	47,105	$ 45,614	41,449	$ 41,698	$ 40,892	$ 41,685
Ending Balance Evaluated for Impairment Under ASC 310-10-35	76,933		61,724
Ending Balance Evaluated for Impairment Under ASC 450-20	4,567,116		3,816,139
Total	4,644,049		3,877,863
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	388		754
Ending Balance Under ASC 450-20	13,522		11,155
Total	13,910	13,064	11,909	11,355	11,927	13,099
Ending Balance Evaluated for Impairment Under ASC 310-10-35	8,386		4,526
Ending Balance Evaluated for Impairment Under ASC 450-20	1,232,570		1,031,554
Total	1,240,956		1,036,080
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	645		636
Ending Balance Under ASC 450-20	17,441		15,262
Total	18,086	17,608	15,898	16,145	14,680	14,152
Ending Balance Evaluated for Impairment Under ASC 310-10-35	43,682		35,771
Ending Balance Evaluated for Impairment Under ASC 450-20	2,018,460		1,671,289
Total	2,062,142		1,707,060
Agricultural and agricultural real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	40		52
Ending Balance Under ASC 450-20	3,899		3,243
Total	3,939	3,676	3,295	3,116	2,788	2,992
Ending Balance Evaluated for Impairment Under ASC 310-10-35	5,916		5,049
Ending Balance Evaluated for Impairment Under ASC 450-20	463,465		418,778
Total	469,381		423,827
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	372		442
Ending Balance Under ASC 450-20	3,474		3,299
Total	3,846	4,099	3,741	3,623	3,815	3,720
Ending Balance Evaluated for Impairment Under ASC 310-10-35	14,024		10,235
Ending Balance Evaluated for Impairment Under ASC 450-20	477,643		370,106
Total	491,667		380,341
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	1,057		813
Ending Balance Under ASC 450-20	6,267		5,793
Total	7,324	$ 7,167	6,606	$ 7,253	$ 7,516	$ 7,722
Ending Balance Evaluated for Impairment Under ASC 310-10-35	4,925		6,143
Ending Balance Evaluated for Impairment Under ASC 450-20	374,978		324,412
Total	$ 379,903		$ 330,555