Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2019

Financial Instruments

Schedule of available-for-sale securities

	December 31, 2019								December 31, 2018
	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	$	22,477	$	—	$	—	$	22,477	$	26,539	$	—	$	—	$	26,539
U.S. Treasury securities		292,506		731		(80)		293,157		76,061		29		(405)		75,685
U.S. agency securities		—		—		—		—		13,017		—		(126)		12,891
Municipal securities		85,638		277		(7)		85,908		18,935		7		(57)		18,885
Total	$	400,621	$	1,008	$	(87)	$	401,542	$	134,552	$	36	$	(588)	$	134,000
Classified as:
Cash equivalents							$	22,477							$	26,539
Short-term investments								379,065								107,461
Total							$	401,542							$	134,000

Change in net unrealized positions of available-for-sale securities and reclassifications from AOCL upon sale

	December 31,
	2019		2018
	(in thousands)
Balance at beginning of year	$	(552)	$	(766)
Net unrealized gains (losses) on available-for-sale securities, net of tax		1,487		171
Reclassifications of losses (gains) realized from sale of available-for-sale securities		(16)		43
Increase (decrease) in other comprehensive loss		1,471		214
Balance at end of year	$	919	$	(552)

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

	December 31, 2019
	Amortized Cost		Fair Value
	(in thousands)
Less than one year	$	141,380	$	141,552
Greater than one year but less than five years		236,764		237,513
Total	$	378,144	$	379,065