Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2014

Fair Value Measurements

Schedule of estimated fair values

	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 March 31, 2014:
U.S. government securities	$	37,116	$	—	$	—	$	37,116
U.S. government agency securities	82,895		27,335		—		110,230
U.S. corporate notes	69,497		19,148		—		88,645
U.S. commercial paper	74,487		—		—		74,487
Money market funds	114,994		—		—		114,994
Total assets measured at estimated fair value	$	378,989	$	46,483	$	—	$	425,472
Liabilities at March 31, 2014:
Convertible subordinated notes due 2023	$	—	$	369,685	$	—	$	369,685

	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, 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