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				67.4		67.4
Other comprehensive income (loss)					(4.8)	(4.8)
Comprehensive income						62.6
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			0.8			0.8
Shares of Class A common stock issued upon the exercise of stock options (in shares)	15,787
Stock-based compensation			8.7			8.7
Stock repurchase				(10.3)		(10.3)
Stock repurchase (in shares)	(130,397)
Net change in restricted stock units			3.3	(7.0)		(3.7)
Net change in restricted and performance stock units (in shares)	75,689
Common stock dividends				(15.2)		(15.2)
Balance at the end of the period at Jun. 30, 2019	$ 2.8	$ 0.6	581.1	475.6	(125.9)	934.2
Balance (in shares) at Jun. 30, 2019	27,657,544	6,279,290
Balance at the beginning of the period at Mar. 31, 2019	$ 2.8	$ 0.6	576.6	452.1	(127.0)	905.1
Balance (in shares) at Mar. 31, 2019	27,710,297	6,279,290
Increase (Decrease) in Stockholders' Equity
Net income				36.4		36.4
Other comprehensive income (loss)					1.1	1.1
Comprehensive income						37.5
Shares of Class A common stock issued upon the exercise of stock options			0.2			0.2
Shares of Class A common stock issued upon the exercise of stock options (in shares)	5,906
Stock-based compensation			4.1			4.1
Stock repurchase				(4.7)		(4.7)
Stock repurchase (in shares)	(55,988)
Net change in restricted stock units			0.2	(0.3)		(0.1)
Net change in restricted and performance stock units (in shares)	(2,671)
Common stock dividends				(7.9)		(7.9)
Balance at the end of the period at Jun. 30, 2019	$ 2.8	$ 0.6	581.1	475.6	(125.9)	934.2
Balance (in shares) at Jun. 30, 2019	27,657,544	6,279,290
Increase (Decrease) in Stockholders' Equity
Change in accounting principle						513.9
Balance at the beginning 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				52.2		52.2
Other comprehensive income (loss)					(7.7)	(7.7)
Comprehensive income						44.5
Shares of Class B common stock converted to Class A common stock (in shares)	50,000	(50,000)
Stock-based compensation			5.4			5.4
Stock repurchase				(21.1)		(21.1)
Stock repurchase (in shares)	(253,535)
Net change in restricted stock units			2.0	(7.8)		(5.8)
Net change in restricted and performance stock units (in shares)	78,952
Common stock dividends				(15.8)		(15.8)
Balance at the end of the period at Jun. 28, 2020	$ 2.8	$ 0.6	598.9	521.4	(138.5)	985.2
Balance (in shares) at Jun. 28, 2020	27,461,833	6,229,290
Balance at the beginning of the period at Mar. 29, 2020	$ 2.8	$ 0.6	597.1	515.5	(148.2)	967.8
Balance (in shares) at Mar. 29, 2020	27,544,757	6,229,290
Increase (Decrease) in Stockholders' Equity
Net income				20.2		20.2
Other comprehensive income (loss)					9.7	9.7
Comprehensive income						29.9
Stock-based compensation			1.8			1.8
Stock repurchase				(6.4)		(6.4)
Stock repurchase (in shares)	(78,828)
Net change in restricted stock units				(0.1)		(0.1)
Net change in restricted and performance stock units (in shares)	(4,096)
Common stock dividends				(7.8)		(7.8)
Balance at the end of the period at Jun. 28, 2020	$ 2.8	$ 0.6	$ 598.9	$ 521.4	$ (138.5)	985.2
Balance (in shares) at Jun. 28, 2020	27,461,833	6,229,290
Increase (Decrease) in Stockholders' Equity
Change in accounting principle						$ 521.4