Earnings Per Share - Summary of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator (in millions):
Net income available to common stockholders	$ 139.1	$ 133.0	$ 93.1
Denominator (in thousands):
Weighted average common shares outstanding	24,851	24,787	24,647
Dilutive effect of stock options and awards	171	195	207
Denominator for diluted earnings per share	25,022	24,982	24,854
Net income per share, basic:	$ 5.6	$ 5.37	$ 3.78
Net income per share, diluted:	$ 5.56	$ 5.32	$ 3.75