Convertible Senior Notes (Liability Component) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Debt Disclosure [Abstract]
Principal	$ 275,000,000		$ 275,000,000
Less: Debt discount, net	(46,445,000)	[1]	(48,891,000)
Net carrying amount	228,555,000		226,109,000
Fair value of Notes	$ 248,400,000
Remaining contractual life	4 years 2 months 12 days

[1] Included in the consolidated balance sheets within convertible senior notes (due 2017) and amortized to interest expense over the remaining life of the Notes using the effective interest rate method.