Allowance for Credit Losses - Credit Risk Profiles by Internally Assigned Grade (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Credit quality
Loans and leases	$ 13,279,097	$ 13,211,650	$ 13,076,191
Loans graded
Credit quality
Loans and leases		6,928,919
Pass
Credit quality
Loans and leases		6,631,021
Special mention
Credit quality
Loans and leases		198,845
Substandard
Credit quality
Loans and leases		99,053
Loss
Credit quality
Loans and leases	0	0
Commercial and Industrial
Credit quality
Loans and leases	3,019,507	2,743,242	3,208,760
Commercial and Industrial | Loans graded
Credit quality
Loans and leases		2,743,242
Commercial and Industrial | Pass
Credit quality
Loans and leases		2,585,908
Commercial and Industrial | Special mention
Credit quality
Loans and leases		91,365
Commercial and Industrial | Substandard
Credit quality
Loans and leases		65,969
Commercial real estate
Credit quality
Loans and leases	3,392,676	3,463,953	2,990,783
Commercial real estate | Loans graded
Credit quality
Loans and leases		3,463,953
Commercial real estate | Pass
Credit quality
Loans and leases		3,327,659
Commercial real estate | Special mention
Credit quality
Loans and leases		106,331
Commercial real estate | Substandard
Credit quality
Loans and leases		29,963
Construction
Credit quality
Loans and leases	735,819	519,241	626,757
Construction | Loans graded
Credit quality
Loans and leases		519,241
Construction | Pass
Credit quality
Loans and leases		515,993
Construction | Special mention
Credit quality
Loans and leases		127
Construction | Substandard
Credit quality
Loans and leases		3,121
Lease financing
Credit quality
Loans and leases	$ 245,411	202,483	$ 147,769
Lease financing | Loans graded
Credit quality
Loans and leases		202,483
Lease financing | Pass
Credit quality
Loans and leases		201,461
Lease financing | Special mention
Credit quality
Loans and leases		$ 1,022