Stock-Based Compensation - Narrative (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		3 Months Ended			6 Months Ended				3 Months Ended		6 Months Ended
	Jun. 30, 2014 Majority shareholder	May 31, 2014 Class A Common Stock	Jun. 30, 2014 Employee Stock option	Mar. 31, 2014 Employee Stock option	Jun. 30, 2013 Employee Stock option	Jun. 30, 2014 Employee Stock option	Jun. 30, 2013 Employee Stock option	Jun. 30, 2014 Employee Stock option Minimum	Jun. 30, 2014 Employee Stock option Maximum	Jun. 30, 2014 Restricted stock units	Jun. 30, 2013 Restricted stock units	Jun. 30, 2014 Restricted stock units	Jun. 30, 2013 Restricted stock units	Jun. 30, 2014 Restricted stock units Minimum	Jun. 30, 2014 Restricted stock units Maximum	Jun. 30, 2014 Employee Stock Class A Common Stock	Jun. 30, 2014 2003 Incentive Compensation Plan	Mar. 31, 2014 2003 Incentive Compensation Plan	Jun. 30, 2014 WMS Equity Compensation Plan	Jun. 30, 2014 ESPP Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period								4 years	5 years					4 years	5 years
Shares available for future issuance																	4,700,000		5,600,000	200,000
Award expiration period						10 years
Number of shares authorized																1,000,000	16,000,000	13,500,000
Percentage of common stock outstanding		40.00%
Maximum employee subscription rate																15.00%
Award offering period																6 months
Discount from market price																15.00%
Grants in period, weighted average grant date fair value			$ 8.86	$ 4.81
Share-based compensation expense			$ 1.0		$ 0.9	$ 1.5	$ 1.8			$ 7.0	$ 4.6	$ 11.6	$ 9.3
Tax benefit from compensation expense			0.4		0.3	0.6	0.7			2.6	1.7	4.3	3.5
Compensation cost not yet recognized			6.7			6.7				49.9		49.9
Compensation cost not yet recognized, period for recognition						2 years						2 years
Increase in stock-based compensation expense	$ 1.9