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

12 Months Ended

Dec. 31, 2017

AVAILABLE-FOR-SALE SECURITIES AND FAIR VALUE MEASUREMENTS

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

	December 31, 2017
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated 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 papers		29,945		—		—			29,945
Money market funds		61,971		—		—			61,971
Total	$	122,727	$	—	$	(18	)	$	122,709

	December 31, 2016
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
U.S. government agencies	$	12,428	$	1	$	—	$	12,429
U.S. commercial papers		72,065		—		—		72,065
Money market funds		64,319		—		—		64,319
Total	$	148,812	$	1	$	—	$	148,813

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

	Estimated Fair Value Measurements as of December 31, 2017 Using:
	Quoted Price in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Types of Instruments (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 papers		—		29,945		—		29,945
Money market funds		61,971		—		—		61,971
Total assets measured at estimated fair value	$	61,971	$	60,738	$	—	$	122,709
Liabilities
Term B Loan	$	—	$	243,750	$	—	$	243,750
2023 Notes		—		241,259		—		241,259
2025 Notes		—		205,975		—		205,975
Total fair value of liabilities	$	—	$	690,984	$	—	$	690,984

	Estimated Fair Value Measurements as of December 31, 2016 Using:
	Quoted Price in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Types of Instruments (In thousands)	Level 1		Level 2		Level 3		Total
Assets
U.S. government agencies	$	—	$	12,429	$	—	$	12,429
U.S. commercial papers		—		72,065		—		72,065
Money market funds		64,319		—		—		64,319
Total assets measured at estimated fair value	$	64,319	$	84,494	$	—	$	148,813
Liabilities
2023 Notes	$	—	$	202,125	$	—	$	202,125
2029 Notes		—		487,189		—		487,189
Total fair value of liabilities	$	—	$	689,314	$	—	$	689,314