Debt - Additional Information (Details) (USD $) In Millions, unless otherwise specified			9 Months Ended
	Sep. 30, 2014	Jun. 30, 2013	Sep. 30, 2014 Senior unsecured credit facility — revolving loan due 2019	Sep. 30, 2014 Senior unsecured credit facility — revolving loan due 2019 Maximum	Sep. 30, 2014 Senior secured credit facility - revolving loan due 2018
Debt Instrument [Line Items]
Face value			$ 700		$ 600
Debt instrument expiration period			2019-09		2018-06
Variable interest rate basis			LIBOR + 1.25%
Spread on variable interest rate basis			1.25%
Pretax charge on unamortized financing costs of credit facility and deferred expense on related interest rate swaps	$ 0.5	$ 1.0
Debt instrument, covenant terms			In accordance with the terms of the new facility, we are required to maintain a minimum interest coverage ratio of 3.50 (based on the ratio of EBITDA, as defined in the credit agreement, to interest expense) and may not exceed a maximum leverage ratio of 3.50 (based on the ratio of total debt to EBITDA) throughout the term of the new facility.
Interest coverage ratio required to be maintained				3.50