Shareholders' Equity (Details) (USD $)	3 Months Ended
	Mar. 31, 2014 Right	Mar. 31, 2013	Dec. 31, 2013	Jun. 30, 2013
Shareholders' Equity [Abstract]
Common stock, shares authorized (in shares)	1,000,000,000		1,000,000,000	680,000,000
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	$ 0	$ 663,542,000
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
Convertible Senior Notes - due April 2020 [Member]
Debt Instrument [Line Items]
Outstanding principal amount	$ 500,000,000		$ 500,000,000
Stated interest rate (in hundredths)	2.00%		2.00%