Consolidated Statements of Stockholders' Equity (USD $) In Millions, except Share data, unless otherwise specified	Class A Common Stock	Class B Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Total
Balance at Dec. 31, 2011	$ 2.9	$ 0.7	$ 420.1	$ 515.1	$ (19.0)	$ 919.8
Balance (in shares) at Dec. 31, 2011	29,471,414	6,953,680
Increase (Decrease) in Stockholders' Equity
Net Income				68.4		68.4
Other comprehensive (loss) income					8.2	8.2
Comprehensive income (loss)						76.6
Shares of Class B common stock converted to Class A common stock	0.1	(0.1)
Shares of Class B common stock converted to Class A common stock (in shares)	365,000	(365,000)
Shares of Class A common stock issued upon the exercise of stock options	0.1		17.7			17.8
Shares of Class A common stock issued upon the exercise of stock options (in shares)	589,798
Stock-based compensation			6.6			6.6
Stock repurchase	(0.2)			(65.6)		(65.8)
Stock repurchase (in shares)	(2,000,000)
Issuance of net shares of restricted Class A common stock				(0.8)		(0.8)
Issuance of net shares of restricted Class A common stock (in shares)	141,767
Net change in restricted stock units			4.3	(3.0)		1.3
Net change in restricted stock units (in shares)	105,660
Common stock dividends				(16.0)		(16.0)
Balance at Dec. 31, 2012	2.9	0.6	448.7	498.1	(10.8)	939.5
Balance (in shares) at Dec. 31, 2012	28,673,639	6,588,680
Increase (Decrease) in Stockholders' Equity
Net Income				58.6		58.6
Other comprehensive (loss) income					22.8	22.8
Comprehensive income (loss)						81.4
Shares of Class B common stock converted to Class A common stock (in shares)	99,390	(99,390)
Shares of Class A common stock issued upon the exercise of stock options			11.9			11.9
Shares of Class A common stock issued upon the exercise of stock options (in shares)	361,094
Stock-based compensation			9.6			9.6
Stock repurchase				(23.0)		(23.0)
Stock repurchase (in shares)	(453,880)
Issuance of net shares of restricted Class A common stock				(1.6)		(1.6)
Issuance of net shares of restricted Class A common stock (in shares)	75,592
Net change in restricted stock units			3.3	(1.3)		2.0
Net change in restricted stock units (in shares)	68,944
Common stock dividends				(17.7)		(17.7)
Balance at Dec. 31, 2013	2.9	0.6	473.5	513.1	12.0	1,002.1
Balance (in shares) at Dec. 31, 2013	28,824,779	6,489,290
Increase (Decrease) in Stockholders' Equity
Net Income				50.3		50.3
Other comprehensive (loss) income					(101.1)	(101.1)
Comprehensive income (loss)						(50.8)
Shares of Class B common stock converted to Class A common stock (in shares)	10,000	(10,000)
Shares of Class A common stock issued upon the exercise of stock options			11.8			11.8
Shares of Class A common stock issued upon the exercise of stock options (in shares)	338,841
Stock-based compensation			8.6			8.6
Stock repurchase				(39.6)		(39.6)
Stock repurchase (in shares)	(669,681)
Issuance of net shares of restricted Class A common stock				(1.6)		(1.6)
Issuance of net shares of restricted Class A common stock (in shares)	12,655
Net change in restricted stock units			3.5	(1.1)		2.4
Net change in restricted stock units (in shares)	35,471
Common stock dividends				(20.5)		(20.5)
Balance at Dec. 31, 2014	$ 2.9	$ 0.6	$ 497.4	$ 500.6	$ (89.1)	$ 912.4
Balance (in shares) at Dec. 31, 2014	28,552,065	6,479,290