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, 2017	$ 2.8	$ 0.6	$ 551.8	$ 372.9	$ (99.1)	$ 829.0
Balance (in shares) at Dec. 31, 2017	27,724,192	6,379,290
Increase (Decrease) in Stockholders' Equity
Change in accounting principle				(0.7)		(0.7)
Net income				28.2		28.2
Other comprehensive income					12.5	12.5
Comprehensive income						40.7
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 (in shares)	4,880
Stock-based compensation			2.7			2.7
Stock repurchase				(6.2)		(6.2)
Stock repurchase (in shares)	(80,055)
Issuance of net shares of restricted Class A common stock				(1.9)		(1.9)
Issuance of net shares of restricted Class A common stock (in shares)	91,968
Net change in restricted stock units			0.9	(2.0)		(1.1)
Net change in restricted stock units (in shares)	61,511
Common stock dividends				(6.7)		(6.7)
Balance at the end of the period at Apr. 01, 2018	$ 2.8	$ 0.6	555.4	383.6	(86.6)	855.8
Balance (in shares) at Apr. 01, 2018	27,852,496	6,329,290
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				31.0		31.0
Other comprehensive income					(5.9)	(5.9)
Comprehensive income						25.1
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			0.6			0.6
Shares of Class A common stock issued upon the exercise of stock options (in shares)	9,881
Stock-based compensation			4.6			4.6
Stock repurchase				(5.6)		(5.6)
Stock repurchase (in shares)	(74,409)
Net change in restricted stock units			3.1	(6.7)		(3.6)
Net change in restricted stock units (in shares)	78,360
Common stock dividends				(7.3)		(7.3)
Balance at the end 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