Derivatives and Hedging Activities - Notional Amounts and Estimated Fair Values of Derivatives (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Sep. 22, 2015
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 454,300,000	$ 404,900,000
Derivative Assets, Estimated Fair Value	10,100,000	8,800,000
Derivative Liability, Notional Amount	467,900,000	433,000,000	$ 100,000,000
Derivative Liabilities, Estimated Fair Value	9,400,000	7,900,000
Not Designated as Hedging Instrument | Interest rate swap contracts
Derivative [Line Items]
Derivative Asset, Notional Amount	403,300,000	344,200,000
Derivative Assets, Estimated Fair Value	8,800,000	7,500,000
Derivative Liability, Notional Amount	403,300,000	344,200,000
Derivative Liabilities, Estimated Fair Value	8,800,000	7,800,000
Not Designated as Hedging Instrument | Interest rate lock commitments
Derivative [Line Items]
Derivative Asset, Notional Amount	51,000,000	60,700,000
Derivative Assets, Estimated Fair Value	1,300,000	1,300,000
Not Designated as Hedging Instrument | Forward loan sales contracts
Derivative [Line Items]
Derivative Liability, Notional Amount	64,600,000	88,800,000
Derivative Liabilities, Estimated Fair Value	$ 600,000	$ 100,000