Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2012

Fair Value Measurements

Estimated fair values of the financial assets

	Estimated Fair Value Measurements at Reporting Date Using:
	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Types of Instruments (in thousands)	Level 1		Level 2		Level 3		Total
Assets at December 31, 2012:
U.S. government securities	$	27,205	$	—	$	—	$	27,205
U.S. government agency securities		56,969		58,497		—		115,466
U.S. corporate notes		40,472		51,094		—		91,566
U.S. commercial paper		—		23,082		—		23,082
Money market funds		78,646		—		—		78,646
Total assets measured at estimated fair value	$	203,292	$	132,673	$	—	$	335,965
Liabilities at December 31 , 2012:
Convertible subordinated notes	$	—	$	194,050	$	—	$	194,050

	Estimated Fair Value Measurements at Reporting Date Using:
	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Types of Instruments (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 estimated fair value	$	163,501	$	72,250	$	—	$	235,751
Liabilities at December 31, 2011:
Convertible subordinated notes	$	—	$	189,588	$	—	$	189,588