Convertible Perpetual Preferred Stock - Textual (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended							1 Months Ended		1 Months Ended	3 Months Ended	12 Months Ended
	Nov. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 11, 2012	Mar. 07, 2011	Oct. 07, 2010	Mar. 07, 2006	Jan. 31, 2014 Subsequent Event [Member]	Jan. 03, 2014 Subsequent Event [Member]	Nov. 30, 2013 Convertible Preferred Stock [Member]	Dec. 31, 2013 Convertible Preferred Stock [Member]	Dec. 31, 2013 Convertible Preferred Stock [Member]	Dec. 31, 2012 Convertible Preferred Stock [Member]	Dec. 31, 2011 Convertible Preferred Stock [Member]	Dec. 31, 2013 2.00% Convertible Senior Subordinated Notes due 2043 [Member]	Nov. 18, 2013 2.00% Convertible Senior Subordinated Notes due 2043 [Member]
Convertible Perpetual Preferred Stock, Shares Issued		96,245	353,355					400,000
Convertible Perpetual Preferred Stock, Liquidation Preference		$ 1,000	$ 1,000
Convertible Perpetual Preferred Stock, Dividend Rate	6.50%	6.50%
Convertible Perpetual Preferred Stock, Terms of Conversion		We may at any time cause the shares of preferred stock to be automatically converted into shares of our common stock at the conversion rate then in effect if the closing sale price of our common stock for 20 trading days within a period of 30 consecutive trading days ending on the trading day before the date we give the notice of forced conversion exceeds 150% of the conversion price of the preferred stock. If we are subject to a fundamental change, as defined in the certificate of designation of the preferred stock, each holder of shares of preferred stock has the right, subject to certain limitations, to require us to purchase with cash any or all of its shares of preferred stock at a purchase price equal to 100% of the accreted liquidation preference, plus any accrued and unpaid dividends to the date of purchase. In addition, if holders of the preferred stock elect to convert shares of preferred stock in connection with certain fundamental changes, we will in certain circumstances increase the conversion rate for such shares of preferred stock.
Convertible Perpetual Preferred Stock, Conversion Price								$ 30.50		$ 30.17
Convertible Perpetual Preferred Stock, Shares Issued Upon Conversion								32.7869		33.1455
Common Stock, Dividends, Per Share, Cash Paid									$ 0.18
Temporary Equity, Repurchased during Period, Shares											257,110	257,110	257,110	46,645
Temporary Equity, Consideration Exchanged for Repurchase													$ 322.8	$ 46.5
Debt Instrument, Principal Amount					275.0	120.0	525.0									320.0	320.0
Temporary Equity, Shares Outstanding												96,245	96,245	353,355	400,000
Temporary Equity, Carrying Amount, Period Increase (Decrease)													249.0	45.2
Capital in Excess of Par Value, Reduction													73.8	1.3
Cumulative dividends included as part of purchase price													2.2	0.5
Preferred Stock Dividends, Dividends Declared		21.0	23.9	26.0									21.0	23.9	26.0
Convertible Perpetual Preferred Stock, Accrued Dividends												$ 1.6	$ 1.6	$ 5.7