Stockholders' Equity Narrative (Details) (USD $) Share data in Millions, unless otherwise specified	1 Months Ended		3 Months Ended		9 Months Ended		1 Months Ended
	Jan. 31, 2013	Apr. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Oct. 31, 2013 Subsequent Event [Member]
Subsequent Event [Line Items]
Stock repurchase program, authorized amount	$ 150,000,000	$ 150,000,000					$ 750,000,000
Shares repurchased during period (in shares)			0.7	1.2	2.8	3.6
Value of shares repurchased during period			29,600,000	36,500,000	112,400,000	111,600,000
Amortization expense from capitalized stock-based compensation			$ 2,200,000	$ 2,000,000	$ 6,100,000	$ 5,700,000