Allowance for Credit Losses - Credit Risk Profiles by Internally Assigned Grade (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Credit quality
Loans and leases	$ 13,499,969,000	$ 13,211,650,000
Loss
Credit quality
Loans and leases	0	0
Commercial and Industrial
Credit quality
Loans and leases	3,170,262,000	2,743,242,000
Commercial and Industrial | Loans graded
Credit quality
Loans and leases		2,743,242,000
Commercial and Industrial | Pass
Credit quality
Loans and leases		2,585,908,000
Commercial and Industrial | Special mention
Credit quality
Loans and leases		91,365,000
Commercial and Industrial | Substandard
Credit quality
Loans and leases		65,969,000
Commercial real estate
Credit quality
Loans and leases	3,461,085,000	3,463,953,000
Commercial real estate | Loans graded
Credit quality
Loans and leases		3,463,953,000
Commercial real estate | Pass
Credit quality
Loans and leases		3,327,659,000
Commercial real estate | Special mention
Credit quality
Loans and leases		106,331,000
Commercial real estate | Substandard
Credit quality
Loans and leases		29,963,000
Construction
Credit quality
Loans and leases	662,871,000	519,241,000
Construction | Loans graded
Credit quality
Loans and leases		519,241,000
Construction | Pass
Credit quality
Loans and leases		515,993,000
Construction | Special mention
Credit quality
Loans and leases		127,000
Construction | Substandard
Credit quality
Loans and leases		3,121,000
Lease financing
Credit quality
Loans and leases	$ 245,977,000	202,483,000
Lease financing | Loans graded
Credit quality
Loans and leases		202,483,000
Lease financing | Pass
Credit quality
Loans and leases		201,461,000
Lease financing | Special mention
Credit quality
Loans and leases		1,022,000
Commercial Lending | Loans graded
Credit quality
Loans and leases		6,928,919,000
Commercial Lending | Pass
Credit quality
Loans and leases		6,631,021,000
Commercial Lending | Special mention
Credit quality
Loans and leases		198,845,000
Commercial Lending | Substandard
Credit quality
Loans and leases		$ 99,053,000