Loan and Lease Financings (Details) (USD $)	9 Months Ended
	Sep. 30, 2013 item	Dec. 31, 2012	Sep. 30, 2012
Loan and Lease Financings
Number of methods to assess credit risk	2
Loan and Lease Financings
Recorded investment in loans and leases	$ 3,468,118,000	$ 3,327,553,000	$ 3,268,413,000
Loan and lease financings excluding residential real estate and consumer loans
Loan and Lease Financings
Recorded investment in loans and leases	2,891,256,000	2,779,639,000
Commercial and agricultural loans
Loan and Lease Financings
Recorded investment in loans and leases	652,180,000	639,069,000	584,996,000
Auto, light truck and environmental equipment
Loan and Lease Financings
Recorded investment in loans and leases	452,405,000	438,147,000	456,665,000
Medium and heavy duty truck
Loan and Lease Financings
Recorded investment in loans and leases	192,974,000	172,002,000	167,709,000
Aircraft financing
Loan and Lease Financings
Recorded investment in loans and leases	704,072,000	696,479,000	685,800,000
Construction equipment financing
Loan and Lease Financings
Recorded investment in loans and leases	315,346,000	278,974,000	276,270,000
Commercial real estate
Loan and Lease Financings
Recorded investment in loans and leases	574,279,000	554,968,000	548,921,000
Credit Quality Grades 1-6 | Loan and lease financings excluding residential real estate and consumer loans
Loan and Lease Financings
Recorded investment in loans and leases	2,765,911,000	2,629,780,000
Credit Quality Grades 1-6 | Commercial and agricultural loans
Loan and Lease Financings
Recorded investment in loans and leases	623,884,000	612,567,000
Credit Quality Grades 1-6 | Auto, light truck and environmental equipment
Loan and Lease Financings
Recorded investment in loans and leases	442,616,000	428,582,000
Credit Quality Grades 1-6 | Medium and heavy duty truck
Loan and Lease Financings
Recorded investment in loans and leases	190,921,000	170,116,000
Credit Quality Grades 1-6 | Aircraft financing
Loan and Lease Financings
Recorded investment in loans and leases	662,126,000	648,316,000
Credit Quality Grades 1-6 | Construction equipment financing
Loan and Lease Financings
Recorded investment in loans and leases	299,938,000	262,980,000
Credit Quality Grades 1-6 | Commercial real estate
Loan and Lease Financings
Recorded investment in loans and leases	546,426,000	507,219,000
Credit Quality Grades 7-12
Loan and Lease Financings
Relationships reviewed quarterly as part of management's evaluation of the appropriateness of the reserve for loan and lease losses	100,000
Credit Quality Grades 7-12 | Loan and lease financings excluding residential real estate and consumer loans
Loan and Lease Financings
Recorded investment in loans and leases	125,345,000	149,859,000
Credit Quality Grades 7-12 | Commercial and agricultural loans
Loan and Lease Financings
Recorded investment in loans and leases	28,296,000	26,502,000
Credit Quality Grades 7-12 | Auto, light truck and environmental equipment
Loan and Lease Financings
Recorded investment in loans and leases	9,789,000	9,565,000
Credit Quality Grades 7-12 | Medium and heavy duty truck
Loan and Lease Financings
Recorded investment in loans and leases	2,053,000	1,886,000
Credit Quality Grades 7-12 | Aircraft financing
Loan and Lease Financings
Recorded investment in loans and leases	41,946,000	48,163,000
Credit Quality Grades 7-12 | Construction equipment financing
Loan and Lease Financings
Recorded investment in loans and leases	15,408,000	15,994,000
Credit Quality Grades 7-12 | Commercial real estate
Loan and Lease Financings
Recorded investment in loans and leases	$ 27,853,000	$ 47,749,000