Securities - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss, Period Increase (Decrease)	$ 0	$ 0	$ 0	$ 0
Debt Securities, Available-for-sale, Allowance for Credit Loss	0		0		$ 0
Debt Securities, Held-to-maturity, Credit Loss Expense (Reversal)	0	0	0	0
Transferred Securities, Unrealized Loss, Before Tax	1,700,000		1,700,000		2,900,000
Securities transferred, Unrealized Loss, Net of Tax	1,400,000		1,400,000		2,300,000
Fair value of securities transferred from AFS to HTM			0		0
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Net gain on sale of securities AFS	1,381,000	$ 78,000	3,399,000	8,281,000
Gross realized gains on AFS securities			3,500,000	8,400,000
Gross realized losses on AFS securities			71,000	89,000
Carrying value of investment securities pledged as collateral	1,480,000,000		1,480,000,000		1,560,000,000
Equity investments	11,794,000		11,794,000		11,905,000
Debt Securities, Held-to-maturity, Sale or Transfer of Investment [Abstract]
Sale of HTM portfolio			0	$ 0
Interest receivable	29,097,000		29,097,000		38,708,000
Debt Securities, Held-to-maturity, Nonaccrual	0		0		0
FHLB stock with other-than-temporary impairment	0		0
Other-than-temporarily impaired equity investments	0		0
Financial Asset, Past Due
Debt Securities, Held-to-maturity, Sale or Transfer of Investment [Abstract]
Securities held to maturity (estimated fair value of $138,879)	0		0		0
Available-for-sale Securities
Debt Securities, Held-to-maturity, Sale or Transfer of Investment [Abstract]
Interest receivable	15,500,000		15,500,000		22,000,000
Held-to-maturity Securities
Debt Securities, Held-to-maturity, Sale or Transfer of Investment [Abstract]
Interest receivable	$ 240,000		$ 240,000		$ 298,000