FAIR VALUE MEASUREMENTS (Tables)

3 Months Ended

Mar. 31, 2013

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, 2013:
U.S. government securities	$	22,170	$	—	$	—	$	22,170
U.S. government agency securities	81,260		71,624		—		152,884
U.S. corporate notes	56,259		26,042		—		82,301
U.S. commercial paper	—		59,120		—		59,120
Money market funds	233,827		—		—		233,827
Total assets measured at estimated fair value	$	393,516	$	156,786	$	—	$	550,302
Liabilities at March 31, 2013:
Convertible subordinated notes due 2015	$	204,413	$	—	$	—	$	204,413
Convertible subordinated notes due 2023	—		313,573		—		313,573
Total convertible subordinated notes	$	204,413	$	313,573	$	—	$	517,986

	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, 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