Loans and Leases (Allowance for credit losses on financing receivables) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	$ 5,925		$ 2,768
Ending Balance Under ASC 450-20	45,831		45,917
Total	51,756	$ 49,738	48,685	$ 45,614	$ 41,854	$ 41,449
Ending Balance Evaluated for Impairment Under ASC 310-10-35	103,243		80,221
Ending Balance Evaluated for Impairment Under ASC 450-20	5,381,516		4,923,645
Total	5,484,759		5,003,866
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	1,342		471
Ending Balance Under ASC 450-20	14,183		15,624
Total	15,525	16,374	16,095	13,064	11,688	11,909
Ending Balance Evaluated for Impairment Under ASC 310-10-35	7,985		6,919
Ending Balance Evaluated for Impairment Under ASC 450-20	1,279,316		1,272,295
Total	1,287,301		1,279,214
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	2,780		698
Ending Balance Under ASC 450-20	20,188		18,834
Total	22,968	20,495	19,532	17,608	16,635	15,898
Ending Balance Evaluated for Impairment Under ASC 310-10-35	53,481		45,442
Ending Balance Evaluated for Impairment Under ASC 450-20	2,590,097		2,280,918
Total	2,643,578		2,326,360
Agricultural and agricultural real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	6		0
Ending Balance Under ASC 450-20	4,094		3,887
Total	4,100	4,028	3,887	3,676	3,216	3,295
Ending Balance Evaluated for Impairment Under ASC 310-10-35	14,359		4,612
Ending Balance Evaluated for Impairment Under ASC 450-20	466,524		467,258
Total	480,883		471,870
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	446		393
Ending Balance Under ASC 450-20	1,619		1,541
Total	2,065	1,851	1,934	4,099	3,745	3,741
Ending Balance Evaluated for Impairment Under ASC 310-10-35	21,710		17,790
Ending Balance Evaluated for Impairment Under ASC 450-20	622,557		521,765
Total	644,267		539,555
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending Balance Under ASC 310-10-35	1,351		1,206
Ending Balance Under ASC 450-20	5,747		6,031
Total	7,098	$ 6,990	7,237	$ 7,167	$ 6,570	$ 6,606
Ending Balance Evaluated for Impairment Under ASC 310-10-35	5,708		5,458
Ending Balance Evaluated for Impairment Under ASC 450-20	423,022		381,409
Total	$ 428,730		$ 386,867