Stock-Based Compensation - Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based compensation
Stock-based compensation expense	$ 13.1	$ 10.0	$ 7.8
Related income tax benefit of stock-based compensation	$ 3.1	$ 2.4	$ 2.0
Employee stock-based compensation plan
Stock-based compensation
Total shares authorized	5,600,000
Shares available for future grants	3,300,000
Non-employee director plan
Stock-based compensation
Total shares authorized	268,941
Shares available for future grants	178,161