Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2012

Fair Value Measurements

Estimated fair values of the financial assets and liabilities

	Estimated Fair Value Measurements at Reporting Date Using:
Types of Instruments	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
(in thousands)	Level 1		Level 2		Level 3		Total
Assets at September 30, 2012:
U.S. government securities	$	30,242	$	—	$	—	$	30,242
U.S. government agency securities	58,893		48,248		—		107,141
U.S. corporate notes	81,160		17,477		—		98,637
U.S. commercial paper	—		37,337		—		37,337
Money market funds	85,634		—		—		85,634
Total assets measured at fair value	$	255,929	$	103,062	$	—	$	358,991
Liabilities at September 30, 2012:
Convertible subordinated notes	$	206,388	$	—	$	—	$	206,388

	Estimated Fair Value Measurements at Reporting Date Using:
Types of Instruments	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
(in thousands)	Level 1		Level 2		Level 3		Total
Assets at December 31, 2011:
U.S. government securities	$	66,174	$	—	$	—	$	66,174
U.S. government agency securities	55,901		37,274		—		93,175
U.S. corporate notes	2,705		—		—		2,705
U.S. commercial paper	—		34,976		—		34,976
Money market funds	38,721		—		—		38,721
Total assets measured at fair value	$	163,501	$	72,250	$	—	$	235,751
Liabilities at December 31, 2011:
Convertible subordinated notes	$	—	$	189,588	$	—	$	189,588