AVAILABLE-FOR-SALE SECURITIES AND FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2019

AVAILABLE-FOR-SALE SECURITIES AND FAIR VALUE MEASUREMENTS

Schedule of amortized cost and estimated fair values for available-for-sale securities

Available-for-sale securities are summarized below:

	December 31, 2019
			Gross		Gross
			Unrealized		Unrealized		Estimated
(In thousands)	Amortized Cost		Gains		Losses		Fair Value
U.S. government securities	$	53,799	$	35		—	$	53,834
U.S. commercial paper		18,915		—		—		18,915
Money market funds		233,992		—		—		233,992
Total	$	306,706	$	35	$	—	$	306,741

	December 31, 2018
			Gross		Gross
			Unrealized		Unrealized		Estimated
(In thousands)	Amortized Cost		Gains		Losses		Fair Value
U.S. government securities	$	29,736	$	—	$	(3)	$	29,733
U.S. government agencies		4,971		—		—		4,971
U.S. corporate notes		2,875		—		—		2,875
U.S. commercial paper		22,037		—		—		22,037
Money market funds		49,358		—		—		49,358
Total	$	108,977	$	—	$	(3)	$	108,974

Schedule of available-for-sale securities measured at fair value on a recurring basis

The estimated fair values were as follows:

	Estimated Fair Value Measurements as of December 31, 2019 Using:
	Quoted Price in		Significant
	Active Markets		Other		Significant
	for Identical		Observable		Unobservable
Types of Instruments	Assets		Inputs		Inputs
(In thousands)	Level 1		Level 2		Level 3		Total
Assets
U.S. government securities	$	—	$	53,834	$	—	$	53,834
U.S. commercial paper		—		18,915		—		18,915
Money market funds		233,992		—		—		233,992
Total assets measured at estimated fair value	$	233,992	$	72,749	$	—	$	306,741
Debt
2023 Notes	$	—	$	243,394	$	—	$	243,394
2025 Notes		—		208,976		—		208,976
Total fair value of debt	$	—	$	452,370	$	—	$	452,370

	Estimated Fair Value Measurements as of December 31, 2018 Using:
	Quoted Price in
	Active Markets		Significant Other		Significant
	for Identical		Observable		Unobservable
Types of Instruments	Assets		Inputs		Inputs
(In thousands)	Level 1		Level 2		Level 3		Total
Assets
U.S. government securities	$	—	$	29,733	$	—	$	29,733
U.S. government agencies		—		4,971		—		4,971
U.S. corporate notes		—		2,875		—		2,875
U.S. commercial paper		—		22,037		—		22,037
Money market funds		49,358		—		—		49,358
Total assets measured at estimated fair value	$	49,358	$	59,616	$	—	$	108,974
Debt
Term B Loan	$	—	$	13,750	$	—	$	13,750
2023 Notes		—		258,918		—		258,918
2025 Notes		—		230,692		—		230,692
Total fair value of debt	$	—	$	503,360	$	—	$	503,360