Allowance for Loan and Lease Losses - Disaggregation by Impairment Methodology (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Allowance for loan and lease losses:
Individually evaluated for impairment	$ 447	$ 494
Collectively evaluated for impairment	138,127	136,759
Total allowance for loan and lease losses	138,574	137,253	$ 135,847	$ 135,494
Loans and leases:
Individually evaluated for impairment	45,552	45,349
Collectively evaluated for impairment	12,418,613	12,232,020
Total loans and leases	12,464,165	12,277,369
Commercial Lending
Loans and leases:
Total loans and leases	6,712,173	6,600,840
Commercial and Industrial
Allowance for loan and lease losses:
Individually evaluated for impairment	4	4
Collectively evaluated for impairment	34,361	34,002
Total allowance for loan and lease losses	34,365	34,006	31,557	33,129
Loans and leases:
Individually evaluated for impairment	17,044	18,183
Collectively evaluated for impairment	3,202,166	3,117,083
Total loans and leases	3,219,210	3,135,266
Commercial Real Estate
Allowance for loan and lease losses:
Individually evaluated for impairment	6	6
Collectively evaluated for impairment	19,248	18,038
Total allowance for loan and lease losses	19,254	18,044	19,932	18,448
Loans and leases:
Individually evaluated for impairment	10,141	10,636
Collectively evaluated for impairment	2,728,416	2,656,961
Total loans and leases	2,738,557	2,667,597
Construction
Allowance for loan and lease losses:
Collectively evaluated for impairment	5,976	6,817
Total allowance for loan and lease losses	5,976	6,817	4,532	4,513
Loans and leases:
Individually evaluated for impairment	2,001
Collectively evaluated for impairment	592,265	632,911
Total loans and leases	594,266	632,911
Lease Financing
Allowance for loan and lease losses:
Collectively evaluated for impairment	585	611
Total allowance for loan and lease losses	585	611	813	847
Loans and leases:
Collectively evaluated for impairment	160,140	165,066
Total loans and leases	160,140	165,066
Residential
Allowance for loan and lease losses:
Individually evaluated for impairment	437	484
Collectively evaluated for impairment	42,783	42,368
Total allowance for loan and lease losses	43,220	42,852	43,541	43,436
Loans and leases:
Individually evaluated for impairment	16,366	16,530
Collectively evaluated for impairment	4,139,637	4,073,523
Total loans and leases	4,156,003	4,090,053
Consumer
Allowance for loan and lease losses:
Collectively evaluated for impairment	30,998	31,249
Total allowance for loan and lease losses	30,998	31,249	27,456	28,388
Loans and leases:
Collectively evaluated for impairment	1,595,989	1,586,476
Total loans and leases	1,595,989	1,586,476
Unallocated
Allowance for loan and lease losses:
Collectively evaluated for impairment	4,176	3,674
Total allowance for loan and lease losses	$ 4,176	$ 3,674	$ 8,016	$ 6,733