Loans and Leases - Loan Acquired (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Acquired loans, outstanding principal	$ 715,390	$ 833,352
Acquired loans, remaining loan mark	(26,703)	(34,790)
Acquired loans, recorded investment	688,687	798,562
Commercial mortgage
Loans and Leases Receivable Disclosure [Line Items]
Acquired loans, outstanding principal	385,801	412,263
Acquired loans, remaining loan mark	(9,965)	(11,213)
Acquired loans, recorded investment	375,836	401,050
Home equity loans and lines
Loans and Leases Receivable Disclosure [Line Items]
Acquired loans, outstanding principal	32,271	37,944
Acquired loans, remaining loan mark	(2,613)	(2,952)
Acquired loans, recorded investment	29,658	34,992
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Acquired loans, outstanding principal	93,916	101,523
Acquired loans, remaining loan mark	(3,127)	(3,572)
Acquired loans, recorded investment	90,789	97,951
Construction
Loans and Leases Receivable Disclosure [Line Items]
Acquired loans, outstanding principal	43,676	86,081
Acquired loans, remaining loan mark	(438)	(1,893)
Acquired loans, recorded investment	43,238	84,188
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Acquired loans, outstanding principal	121,265	141,960
Acquired loans, remaining loan mark	(8,876)	(11,952)
Acquired loans, recorded investment	112,389	130,008
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Acquired loans, outstanding principal	1,669	3,051
Acquired loans, remaining loan mark	(35)	(44)
Acquired loans, recorded investment	1,634	3,007
Leases
Loans and Leases Receivable Disclosure [Line Items]
Acquired loans, outstanding principal	36,792	50,530
Acquired loans, remaining loan mark	(1,649)	(3,164)
Acquired loans, recorded investment	$ 35,143	$ 47,366