Investment Securities - Narrative (Details)	3 Months Ended
	Mar. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security	Mar. 31, 2019 USD ($)
Investment Securities
Accumulated other comprehensive income (loss) before tax amount	$ 62,200,000	$ 30,100,000
Accumulated other comprehensive income (loss), net of tax	$ 44,409,000	$ 21,523,000
Available-for-sale and held-to-maturity securities in nonaccrual status | security	0
Available-for-sale and held-to-maturity securities purchased with deterioration in credit quality | security	0	0
Available-for-sale and held-to-maturity collateral dependant | security	0
Gross gains	$ 8,000,000.0	$ 3,800,000	$ 1,000,000.0
Gross losses	204,000	147,000	615,000
Proceeds from available-for-sale securities	155,300,000	133,300,000	168,800,000
Receivables for securities with a later settlement date	57,400,000
Investment securities pledged	111,500,000	$ 125,700,000
FHLB stock	17,300,000
FRB stock	51,700,000
Other stock	23,900,000
Amount of stock repurchased by FHLB	10,300,000		$ 12,900,000
Impairment loss on investments in FHLB, FRB and other stock	$ 0