Acquisitions - Summary of Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 0.85	$ 1.02	$ 2.60	$ 1.63
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 0.85	$ 1.02	$ 2.60	$ 1.63
Great Western Bank
Business Acquisition [Line Items]
Total revenues	$ 314.0	$ 295.8	$ 883.5	$ 909.1
Net income	$ 90.3	$ 110.9	$ 267.8	$ 177.0