Allowance for Loan and Lease Losses - Recorded Investment in Loans and Leases (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 4,806,306	$ 4,672,909
Originated Loans and Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	13,073	12,350
Collectively evaluated for impairment	4,521,765	4,349,982
Total	4,534,838	4,362,332
Total Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	3,441	3,471
Loans acquired with deteriorated credit quality	11,309	11,962
Collectively evaluated for impairment	256,718	295,144
Total	271,468	310,577
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,065,385	1,091,651
Commercial and industrial | Originated Loans and Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	3,928	1,759
Collectively evaluated for impairment	1,017,166	1,038,916
Total	1,021,094	1,040,675
Commercial and industrial | Total Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	261	276
Loans acquired with deteriorated credit quality	209	506
Collectively evaluated for impairment	43,821	50,194
Total	44,291	50,976
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	2,321,158	2,200,727
Commercial Real Estate | Originated Loans and Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	5,136	6,626
Collectively evaluated for impairment	2,132,877	1,986,354
Total	2,138,013	1,992,980
Commercial Real Estate | Total Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	1,400	1,372
Loans acquired with deteriorated credit quality	5,974	7,481
Collectively evaluated for impairment	175,771	198,894
Total	183,145	207,747
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,338,406	1,302,941
Residential real estate | Originated Loans and Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	4,009	3,965
Collectively evaluated for impairment	1,291,224	1,247,887
Total	1,295,233	1,251,852
Residential real estate | Total Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	1,780	1,823
Loans acquired with deteriorated credit quality	5,126	3,975
Collectively evaluated for impairment	36,267	45,291
Total	43,173	51,089
Consumer and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	67,302	63,123
Consumer and other | Originated Loans and Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	66,443	62,358
Total	66,443	62,358
Consumer and other | Total Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	0	0
Loans acquired with deteriorated credit quality	0	0
Collectively evaluated for impairment	859	765
Total	859	765
Finance Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	14,055	14,467
Finance Leases | Originated Loans and Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	14,055	14,467
Total	14,055	14,467
Finance Leases | Total Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Covered loans | Total Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	0	0
Loans acquired with deteriorated credit quality	0	0
Collectively evaluated for impairment	0	0
Total	$ 0	$ 0