Convertible Senior Notes Components of consolidated balance sheets associated with convertible senior notes (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 3.625% Convertible Senior Notes Due 2025 [Member]	Dec. 31, 2012 3.625% Convertible Senior Notes Due 2025 [Member]	May 31, 2012 3.625% Convertible Senior Notes Due 2025 [Member]	May 31, 2005 3.625% Convertible Senior Notes Due 2025 [Member]	Dec. 31, 2013 5.875% Convertible Senior Notes Due 2035 [Member]	Dec. 31, 2012 5.875% Convertible Senior Notes Due 2035 [Member]	Nov. 30, 2005 5.875% Convertible Senior Notes Due 2035 [Member]	May 31, 2005 5.875% Convertible Senior Notes Due 2035 [Member]
Debt Instrument [Line Items]
Face amount			$ 450,000	$ 450,000		$ 250,000,000.0	$ 139,467,000	$ 139,467,000	$ 300,000,000.0
Discount	(43,983,000)	(44,582,000)
Net carrying value	95,934,000	95,335,000
Carrying amount of equity component included in additional paid-in capital	108,714,000	108,714,000
Excess of instruments’ if-converted values over face principal amounts	$ 0	$ 0
Interest rate on notes			3.625%		3.625%	3.625%	5.875%	5.875%	5.875%	5.875%