Loans (Not Covered by Share Agreements (Past Due Financing Receivables)) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 19,945	$ 15,348
Current	5,269,458	4,948,863
Nonaccrual	64,299	39,655
Total	5,353,702	5,003,866
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,653	11,561
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9,206	3,787
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	86	0
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,238	8,239
Current	3,794,310	3,575,730
Nonaccrual	25,299	21,605
Total	3,825,847	3,605,574
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,423	2,613
Current	1,281,241	1,273,678
Nonaccrual	4,601	2,923
Total	1,287,265	1,279,214
Commercial | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,815	5,626
Current	2,513,069	2,302,052
Nonaccrual	20,698	18,682
Total	2,538,582	2,326,360
Commercial | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,013	5,554
Commercial | 30-59 Days Past Due | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,127	2,005
Commercial | 30-59 Days Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	886	3,549
Commercial | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,148	2,685
Commercial | 60-89 Days Past Due | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	219	608
Commercial | 60-89 Days Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,929	2,077
Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	77	0
Commercial | 90 Days or More Past Due | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	77	0
Commercial | 90 Days or More Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Agricultural and agricultural real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,390	197
Current	472,597	470,455
Nonaccrual	13,331	1,218
Total	489,318	471,870
Agricultural and agricultural real estate | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	199	143
Agricultural and agricultural real estate | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,191	54
Agricultural and agricultural real estate | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,832	2,015
Current	590,626	523,915
Nonaccrual	21,466	13,625
Total	617,924	539,555
Residential real estate | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,986	1,900
Residential real estate | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	846	115
Residential real estate | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,485	4,897
Current	411,925	378,763
Nonaccrual	4,203	3,207
Total	420,613	386,867
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,455	3,964
Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,021	933
Consumer | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 9	$ 0