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

12 Months Ended

Dec. 31, 2018

AVAILABLE-FOR-SALE SECURITIES AND FAIR VALUE MEASUREMENTS

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

	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

	December 31, 2017
			Gross		Gross
			Unrealized		Unrealized		Estimated
(In thousands)	Amortized Cost		Gains		Losses		Fair Value
U.S. government securities	$	9,943	$	—	$	(1)	$	9,942
U.S. government agencies		9,987		—		(2)		9,985
U.S. corporate notes		10,881		—		(15)		10,866
U.S. commercial paper		29,945		—		—		29,945
Money market funds		61,971		—		—		61,971
Total	$	122,727	$	—	$	(18)	$	122,709

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

	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

	Estimated Fair Value Measurements as of December 31, 2017 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	$	—	$	9,942	$	—	$	9,942
U.S. government agencies		—		9,985		—		9,985
U.S. corporate notes		—		10,866		—		10,866
U.S. commercial paper		—		29,945		—		29,945
Money market funds		61,971		—		—		61,971
Total assets measured at estimated fair value	$	61,971	$	60,738	$	—	$	122,709
Debt
Term B Loan	$	—	$	243,750	$	—	$	243,750
2023 Notes		—		241,259		—		241,259
2025 Notes		—		205,975		—		205,975
Total fair value of debt	$	—	$	690,984	$	—	$	690,984