Available-for-Sale Securities and Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2019

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

	June 30, 2019
			Gross		Gross
			Unrealized		Unrealized		Estimated
(In thousands)	Amortized Cost		Gains		Losses		Fair Value
U.S. government securities	$	49,012	$	25	$	—	$	49,037
U.S. government agencies		19,919		8		—		19,927
U.S. commercial paper		38,747		—		—		38,747
Money market funds		120,581		—		—		120,581
Total	$	228,259	$	33	$	—	$	228,292

	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

	Estimated Fair Value Measurements as of June 30, 2019 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	$	—	$	49,037	$	—	$	49,037
U.S. government agencies		—		19,927		—		19,927
U.S. commercial paper		—		38,747		—		38,747
Money market funds		120,581		—		—		120,581
Total assets measured at estimated fair value	$	120,581	$	107,711	$	—	$	228,292
Debt
Term B Loan	$	—	$	13,750	$	—	$	13,750
2023 Notes		—		252,754		—		252,754
2025 Notes		—		208,181		—		208,181
Total fair value of debt	$	—	$	474,685	$	—	$	474,685

	Estimated Fair Value Measurements as of December 31, 2018 Using:
Types of Instruments	Quoted Price in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable 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