FAIR VALUE MEASUREMENTS (Tables)

6 Months Ended

Jun. 30, 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 June 30, 2013:
U.S. government securities	$	27,116	$	—	$	—	$	27,116
U.S. government agency securities	113,583		44,346		—		157,929
U.S. corporate notes	91,871		12,200		—		104,071
U.S. commercial paper	4,989		39,978		—		44,967
Money market funds	192,694		—		—		192,694
Total assets measured at estimated fair value	$	430,253	$	96,524	$	—	$	526,777
Liabilities at June 30, 2013:
Convertible subordinated notes due 2015	$	268,596	$	—	$	—	$	268,596
Convertible subordinated notes due 2023	443,920		—		—		443,920
Total convertible subordinated notes	$	712,516	$	—	$	—	$	712,516

	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