Long Term Obligations (Convertible Senior Subordinated Notes) (Details) - USD ($)		1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 17, 2013	Sep. 30, 2010	Jun. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Convertible Senior Subordinated Notes
Rental expense				$ 18,100,000	$ 38,900,000	$ 57,700,000
Convertible Senior Subordinated Notes 3.35 Percent Due 2015
Convertible Senior Subordinated Notes
Convertible senior subordinated notes		$ 400,000,000.0
Interest rate (percent)		3.35%
Net proceeds from convertible debt offering		$ 391,600,000
Underwriting discount		$ 8,400,000
Conversion price (usd per share)		$ 48.83
Conversion ratio, shares of common stock per principal amount		0.0204794
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
Redemption price (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			$ 0.01675
Converted instrument, shares issued			87,109
Interest expense			$ 6,700,000
Offset to additional paid-in capital			$ 4,200,000