Allowance for Loan and Lease Losses - Disaggregation by Impairment Methodology (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Allowance for loan and lease losses:
Individually evaluated for impairment	$ 453		$ 494
Collectively evaluated for impairment	140,148		136,759
Total allowance for loan and lease losses	140,601	$ 138,574	137,253	$ 136,883	$ 135,847	$ 135,494
Loans and leases:
Individually evaluated for impairment	45,720		45,349
Collectively evaluated for impairment	12,591,966		12,232,020
Total loans and leases	12,637,686		12,277,369
Commercial Lending
Loans and leases:
Total loans and leases	6,769,515		6,600,840
Commercial and Industrial
Allowance for loan and lease losses:
Individually evaluated for impairment	38		4
Collectively evaluated for impairment	35,201		34,002
Total allowance for loan and lease losses	35,239	34,365	34,006	33,341	31,557	33,129
Loans and leases:
Individually evaluated for impairment	16,084		18,183
Collectively evaluated for impairment	3,100,061		3,117,083
Total loans and leases	3,116,145		3,135,266
Commercial Real Estate
Allowance for loan and lease losses:
Individually evaluated for impairment	6		6
Collectively evaluated for impairment	20,501		18,038
Total allowance for loan and lease losses	20,507	19,254	18,044	20,011	19,932	18,448
Loans and leases:
Individually evaluated for impairment	9,903		10,636
Collectively evaluated for impairment	2,827,617		2,656,961
Total loans and leases	2,837,520		2,667,597
Construction
Allowance for loan and lease losses:
Collectively evaluated for impairment	7,606		6,817
Total allowance for loan and lease losses	7,606	5,976	6,817	5,471	4,532	4,513
Loans and leases:
Individually evaluated for impairment	2,238
Collectively evaluated for impairment	651,846		632,911
Total loans and leases	654,084		632,911
Lease Financing
Allowance for loan and lease losses:
Collectively evaluated for impairment	557		611
Total allowance for loan and lease losses	557	585	611	857	813	847
Loans and leases:
Collectively evaluated for impairment	161,766		165,066
Total loans and leases	161,766		165,066
Residential
Allowance for loan and lease losses:
Individually evaluated for impairment	409		484
Collectively evaluated for impairment	43,516		42,368
Total allowance for loan and lease losses	43,925	43,220	42,852	44,374	43,541	43,436
Loans and leases:
Individually evaluated for impairment	17,495		16,530
Collectively evaluated for impairment	4,218,588		4,073,523
Total loans and leases	4,236,083		4,090,053
Consumer
Allowance for loan and lease losses:
Collectively evaluated for impairment	31,509		31,249
Total allowance for loan and lease losses	31,509	30,998	31,249	27,903	27,456	28,388
Loans and leases:
Collectively evaluated for impairment	1,632,088		1,586,476
Total loans and leases	1,632,088		1,586,476
Unallocated
Allowance for loan and lease losses:
Collectively evaluated for impairment	1,258		3,674
Total allowance for loan and lease losses	$ 1,258	$ 4,176	$ 3,674	$ 4,926	$ 8,016	$ 6,733