Convertible Senior Subordinated Notes (Details) (Convertible Senior Subordinated Notes 3.35 Percent Due 2015, USD $)	0 Months Ended	3 Months Ended	12 Months Ended
	Jun. 17, 2013	Jun. 30, 2013	Dec. 31, 2010
Convertible Senior Subordinated Notes 3.35 Percent Due 2015
Convertible Senior Subordinated Notes
Convertible senior subordinated notes			$ 400,000,000.0
Interest rate (as a percent)			3.35%
Net proceeds from convertible debt offering			391,600,000
Underwriting discount			8,400,000
Conversion price (in dollars per share)		$ 48.83	$ 48.83
Original conversion rate, number of shares to be issued per $1000 of principal (in shares)			20.4794
Convertible debt principal amount, basis for exchange		1,000	1,000
Percent closing price needs to exceed the conversion price for at least 20 trading days within 30 consecutive trading days for provisional redemption (as a percent)		130.00%
Minimum number of days within 30 consecutive trading days the closing price needs to exceed the conversion price for provisional redemption (in days)		20 days
Total consecutive trading days during which the closing price must exceed the conversion price for at least 20 trading days for provisional redemption (in days)		30 days
Percentage of principal amount redeemed (percent)			100.00%
Amount of converted instrument		399,800,000
Convertible senior subordinated notes (due 2015) conversion (shares)		8,188,448
Value of redeemed or called stock during period	200,000
Redemption premium (usd per share)		16.75
Converted instrument, shares issued (shares)		87,109
Interest expense		6,700,000
Convertible debt with conversion feature		$ 4,200,000