Nature of Operations and Summary of Significant Accounting Policies - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Nature of Operations and Summary of Significant Accounting Policies
Net income and net income available to common shareholders	$ 59,313	$ 73,612	$ 67,109
Average common shares outstanding	14,043	14,201	14,132
Average common share stock options outstanding	61	129	128
Average diluted common shares	14,104	14,330	14,260
Earnings per common share - basic	$ 4.22	$ 5.18	$ 4.75
Earnings per common share - diluted	$ 4.21	$ 5.14	$ 4.71