Borrowing Arrangements Additional Information (Details) (USD $)	6 Months Ended	1 Months Ended
	Jul. 31, 2014	Dec. 31, 2012 Senior Notes	Jul. 31, 2014 Senior Notes	Dec. 31, 2012 Senior Notes Senior Notes 2017	Dec. 31, 2012 Senior Notes Senior Notes 2022
Debt Instrument [Line Items]
Debt instrument, face amount				$ 400,000,000	$ 350,000,000
Debt instrument, interest rate, stated percentage				1.95%	3.60%
Proceeds from debt, net of issuance costs		739,300,000
Debt instrument, unamortized discount		4,500,000
Debt issuance cost		6,100,000
Debt issuance redemption discount premium, percentage of principle amount		101.00%
Debt fair value			749,500,000
Line of credit facility, maximum borrowing capacity	400,000,000
Line of credit facility, additional borrowings available	100,000,000.0
Line of credit facility, expiration date	May 31, 2018
Line of credit facility, outstanding borrowings	$ 0