Debt - Line of Credit (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 27, 2014
Debt Disclosure [Abstract]
Interest Paid	$ 3.7	$ 2.1	$ 4.3
Line of Credit Facility [Line Items]
Line of Credit Facility, Available Additional Borrowing Capacity	300
Credit Agreement [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				300
Credit Agreement [Member] | Adjusted Base Rate Advances [Member] | Adjusted Base Rate [Member] | Federal Funds Rate [Member] | Minimum [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Basis Spread on Variable Rate	0.50%
Credit Agreement [Member] | Adjusted Base Rate Advances [Member] | Adjusted Base Rate [Member] | Eurodollar Rate [Member] | Minimum [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Basis Spread on Variable Rate	1.00%
Credit Agreement [Member] | Adjusted Base Rate Advances [Member] | Applicable Margin [Member] | Minimum [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Basis Spread on Variable Rate	0.125%
Credit Agreement [Member] | Adjusted Base Rate Advances [Member] | Applicable Margin [Member] | Maximum [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Basis Spread on Variable Rate	0.75%
Credit Agreement [Member] | Eurodollar Advances [Member] | Applicable Margin [Member] | Minimum [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Basis Spread on Variable Rate	1.125%
Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 500
Letter of Credit [Member] | Eurodollar Advances [Member] | Applicable Margin [Member] | Maximum [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Basis Spread on Variable Rate	1.75%