Shareholders' Equity (Details) (USD $)	3 Months Ended	6 Months Ended
	Mar. 31, 2013 Right	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Convertible Debentures [Member]	Dec. 31, 2012 Convertible Debentures [Member]	Jun. 30, 2013 Convertible Senior Notes [Member]	Dec. 31, 2012 Convertible Senior Notes [Member]	Jun. 30, 2013 Convertible Senior Notes - due April 2020 [Member]	Mar. 31, 2013 Convertible Senior Notes - due April 2020 [Member]
Shareholders' Equity [Abstract]
Sale of common stock (in shares)	135,000,000
Sale of common stock, price per share (in dollars per share)	$ 5.15
Sale of common stock, net proceeds	$ 663,542,000	$ 663,392,000	$ 0
Debt Instrument [Line Items]
Outstanding principal amount				389,500,000	389,500,000	345,000,000	345,000,000	500,000,000	500,000,000
Stated interest rate (in hundredths)				9.00%	9.00%	5.00%	5.00%	2.00%	2.00%
Contribution to subsidiary	$ 800,000,000	$ 800,000,000
Shareholder Rights Agreement [Abstract]
Shareholder rights accompanying each outstanding share of the company's common stock (in number of Rights)	1
Distribution date, description	the earlier of ten days after a public announcement that a person has become an Acquiring Person, or ten business days after a person announces or begins a tender offer in which consummation of such offer would result in a person becoming an Acquiring Person.
Common stock, beneficial ownership threshold to be considered an Acquiring Person (in hundredths)	5.00%
Common shares purchasable per Right (in shares)	0.10
Purchase price (in dollars per share)	$ 14
Purchase price (in dollars per one-tenth share)	$ 1.40
Redemption price (in dollars per Right)	$ 0.001