Long-term Debt Covenants & Guarantees (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Credit Agreement [Member]
Line of Credit Facility, Covenant Compliance	the Company was in compliance with the covenants under the Credit Agreement, as amended by Amendment No. 1 and Amendment No. 2 (the Amendments)
Credit Agreement [Member] | Increase in Level of Leverage Ratio [Member]
Debt Instrument, Covenant Description	0.50
Credit Agreement [Member] | Maximum Total Leverage Ratio [Member]
Debt Instrument, Covenant Description	greater than or equal to 4.00 to 1.00
Class A Common Stock [Member]
Stock Repurchase Program, Authorized Amount	$ 300.0
Base Rate [Member] | Credit Agreement [Member]
Debt Instrument, Basis Spread on Variable Rate	2.25%
LIBOR Interest Rate [Member] | Credit Agreement [Member]
Debt Instrument, Basis Spread on Variable Rate	1.25%
Maximum [Member] | Credit Agreement [Member] | Maximum Total Leverage Ratio [Member]
Debt Instrument, Covenant Description	4.50 to 1.00
Maximum [Member] | December 31, 2016 through September 30, 2017 | Credit Agreement [Member] | Maximum Total Leverage Ratio [Member]
Debt Instrument, Covenant Description	4.50 to 1.00
Maximum [Member] | December 31, 2017 through March 31, 2018 | Credit Agreement [Member] | Maximum Total Leverage Ratio [Member]
Debt Instrument, Covenant Description	3.75 to 1.00
Maximum [Member] | June 30, 2018 through March 31, 2020 | Credit Agreement [Member] | Maximum Total Leverage Ratio [Member]
Debt Instrument, Covenant Description	3.50 to 1.00
Maximum [Member] | Pro Forma [Member] | Credit Agreement [Member] | Maximum Total Leverage Ratio [Member]
Debt Instrument, Covenant Description	4.00 to 1.00
Maximum [Member] | Base Rate [Member] | Credit Agreement [Member]
Debt Instrument, Basis Spread on Variable Rate	1.00%
Minimum [Member] | Credit Agreement [Member]
Cash and available revolving credit capacity	$ 150.0
Minimum [Member] | Pro Forma [Member] | Credit Agreement [Member] | Maximum Total Leverage Ratio [Member]
Debt Instrument, Covenant Description	3.00 to 1.00
Minimum [Member] | Base Rate [Member] | Credit Agreement [Member]
Debt Instrument, Basis Spread on Variable Rate	0.00%