Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Class A Common Stock	Class B Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Total
Balance at the beginning of the period at Dec. 31, 2018	$ 2.8	$ 0.6	$ 568.3	$ 440.7	$ (121.1)	$ 891.3
Balance (in shares) at Dec. 31, 2018	27,646,465	6,329,290
Increase (Decrease) in Stockholders' Equity
Net income				131.5		131.5
Other comprehensive income					(9.7)	(9.7)
Comprehensive income						121.8
Shares of Class B common stock converted to Class A common stock (in shares)	50,000	(50,000)
Shares of Class A common stock issued upon the exercise of stock options			2.1			2.1
Shares of Class A common stock issued upon the exercise of stock options (in shares)	38,288
Stock-based compensation			17.8			17.8
Stock repurchase				(19.5)		(19.5)
Stock repurchase (in shares)	(227,620)
Net change in restricted stock and performance stock units			3.3	(7.4)		(4.1)
Net change in restricted and performance stock units (in shares)	79,283
Common stock dividends				(31.4)		(31.4)
Balance at the end of the period at Dec. 31, 2019	$ 2.8	$ 0.6	591.5	513.9	(130.8)	978.0
Balance (in shares) at Dec. 31, 2019	27,586,416	6,279,290
Increase (Decrease) in Stockholders' Equity
Net income				114.3		114.3
Other comprehensive income					30.8	30.8
Comprehensive income						145.1
Shares of Class B common stock converted to Class A common stock (in shares)	135,000	(135,000)
Shares of Class A common stock issued upon the exercise of stock options			0.4			0.4
Shares of Class A common stock issued upon the exercise of stock options (in shares)	4,666
Stock-based compensation			12.7			12.7
Stock repurchase				(28.9)		(28.9)
Stock repurchase (in shares)	(331,531)
Net change in restricted stock and performance stock units			1.7	(7.8)		(6.1)
Net change in restricted and performance stock units (in shares)	83,961
Common stock dividends				(31.4)		(31.4)
Balance at the end of the period at Dec. 31, 2020	$ 2.8	$ 0.6	606.3	560.1	(100.0)	1,069.8
Balance (in shares) at Dec. 31, 2020	27,478,512	6,144,290
Increase (Decrease) in Stockholders' Equity
Net income				165.7		165.7
Other comprehensive income					(27.3)	(27.3)
Comprehensive income						138.4
Shares of Class B common stock converted to Class A common stock (in shares)	120,000	(120,000)
Shares of Class A common stock issued upon the exercise of stock options			0.1			0.1
Shares of Class A common stock issued upon the exercise of stock options (in shares)	1,440
Stock-based compensation			22.9			22.9
Stock repurchase				(16.0)		(16.0)
Stock repurchase (in shares)	(109,998)
Net change in restricted stock and performance stock units			1.9	(9.6)		(7.7)
Net change in restricted and performance stock units (in shares)	94,571
Common stock dividends				(34.3)		(34.3)
Balance at the end of the period at Dec. 31, 2021	$ 2.8	$ 0.6	$ 631.2	$ 665.9	$ (127.3)	$ 1,173.2
Balance (in shares) at Dec. 31, 2021	27,584,525	6,024,290