Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2020

Financial Instruments

Schedule of available-for-sale securities

	March 31, 2020								December 31, 2019
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Estimated Fair Value		Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Estimated Fair Value
	(in thousands)
Money market deposits	$	35,818	$	—	$	—	$	35,818	$	22,477	$	—	$	—	$	22,477
U.S. Treasury securities		243,821		5,493		—		249,314		292,506		731		(80)		293,157
Municipal securities		82,214		195		(42)		82,367		85,638		277		(7)		85,908
Total	$	361,853	$	5,688	$	(42)	$	367,499	$	400,621	$	1,008	$	(87)	$	401,542
Classified as:
Cash equivalents							$	35,818							$	22,477
Short-term investments								331,681								379,065
Total							$	367,499							$	401,542

Summarized portfolio of available-for-sale securities by contractual maturity

	March 31, 2020
	Amortized Cost		Fair Value
	(in thousands)
Less than one year	$	127,898	$	128,675
Greater than one year but less than five years		198,137		203,006
Total	$	326,035	$	331,681