Derivative Instruments and Hedging Activities - Value of Derivative Assets and Derivative Liabilities (Details) - Not Designated as Hedging Instruments - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Other Assets
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	$ 7,448	$ 3,074
Other Assets | Interest rate swap contracts—commercial loans
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	7,448	3,074
Notional amount, Derivatives (included in Other Assets)	247,817	263,841
Collateral received/posted, Derivatives	5,530	0
Other Assets | Interest rate lock commitments—mortgage loans
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	229	226
Notional amount, Derivatives (included in Other Assets)	9,084	6,860
Other Assets | Forward sale contracts—mortgage loans
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Assets)	61	0
Notional amount, Derivatives (included in Other Assets)	11,250	0
Other Liabilities
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Liabilities)	7,483	3,055
Other Liabilities | Interest rate swap contracts—commercial loans
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Liabilities)	7,483	3,055
Notional amount, Derivatives (included in Other Liabilities)	247,817	263,841
Collateral received/posted, Derivatives	0	1,448
Other Liabilities | Interest rate lock commitments—mortgage loans
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Liabilities)	0	0
Notional amount, Derivatives (included in Other Liabilities)	0	0
Other Liabilities | Forward sale contracts—mortgage loans
Derivatives not Designated as Hedging Instruments
Fair value, Derivatives (included in Other Liabilities)	0	5
Notional amount, Derivatives (included in Other Liabilities)	$ 0	$ 6,580