Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2013

Fair Value Measurements

Schedule of estimated fair values

	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, 2013:
U.S. government securities	$	42,158	$	—	$	—	$	42,158
U.S. government agency securities		98,236		43,095		—		141,331
U.S. corporate notes		61,591		33,386		—		94,977
U.S. commercial paper		3,499		98,523		—		102,022
Money market funds		122,343		—		—		122,343
Total assets measured at estimated fair value	$	327,827	$	175,004	$	—	$	502,831
Liabilities at December 31, 2013:
Convertible subordinated notes due 2023	$	—	$	408,250	$	—	$	408,250

	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 due 2015	$	—	$	194,050	$	—	$	194,050