Securities Securities - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2018	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities transferred to held-to-maturity portfolio	$ 0	$ 873,613,000	$ 179,800,000
Unrealized after tax gain (loss) on available for sale securities transferred to the held to maturity portfolio		69,000,000.0	$ (2,200,000)
Securities pledged as collateral to secure public funds and other deposits or securities sold under agreements to repurchase	609,800,000
Secured borrowing under agreement to repurchase	172,100,000
Accumulated unrealized losses	29,897,000			$ 17,837,000
Fair value of securities	1,229,973,000			871,433,000
Allowance for credit losses - securities held-to-maturity	(198,000)			$ (191,000)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	342,000
Proceeds from Sale of Available-for-sale Securities	0	$ 30,204,000
Securities pledged as collateral
Debt Securities, Available-for-sale [Line Items]
Secured borrowing under agreement to repurchase	$ 172,100,000