8. Debt

The carrying amount and fair value of our convertible notes are as follows (in thousands):

	March 31, 2013				December 31, 2012
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Pfizer convertible subordinated note due 2014	$	9,159	$	18,784	$	9,033	$	13,573
4.75% convertible senior notes due 2015	328,354		1,079,915		322,043		798,040
	$	337,513	$	1,098,699	$	331,076	$	811,613

The fair values of the 4.75% Convertible Senior Notes due 2015 (the “4.75% Senior Notes”) are based on quoted prices in an active market and, therefore, these convertible senior notes are classified within Level 1 in the fair value hierarchy. The fair value of the convertible subordinated note issued to Pfizer (the “Pfizer Note”) is based on a fair value model that incorporates both observable and unobservable inputs, including the quoted price of our common stock and an estimated discount rate, and, therefore, the Pfizer Note is classified as Level 3 in the fair value hierarchy.