Fair Value Measurement (Tables)

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Schedule of Assets and Liabilities Measured at Fair Value

Assets and liabilities measured at fair value on a recurring basis consist of the following as of March 31, 2019 (in thousands):

			Fair Value Measurements at Reporting Date Using
	March 31, 2019		Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Money market funds	$	9,441	$	9,441	$	—	$	—
Marketable securities:
Corporate debt securities	47,691		—		47,691		—
Tax-exempt municipal securities	19,043		—		19,043		—
Variable rate demand notes	1,600		—		1,600		—
Commercial paper	1,018		—		1,018		—
Total assets at fair value on a recurring basis	$	78,793	$	9,441	$	69,352	$	—
Liabilities:
Deferred payments	$	4,131	$	—	$	—	$	4,131

Assets and liabilities measured at fair value on a recurring basis consist of the following as of December 31, 2018 (in thousands):

			Fair Value Measurements at Reporting Date Using
	December 31, 2018		Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Money market funds	$	1,791	$	1,791	$	—	$	—
Marketable securities:
Corporate debt securities	48,430		—		48,430		—
Tax-exempt municipal securities	22,869		—		22,869		—
Variable rate demand notes	4,000		—		4,000		—
Total assets at fair value on a recurring basis	77,090		1,791		75,299		—
Liabilities:
Deferred payments	$	4,120	$	—	$	—	$	4,120

Schedule of Changes in Fair Value of Level 3 Liability

Changes in the fair value of the Company’s Level 3 liabilities during the three months ended March 31, 2018 and 2019 are as follows (in thousands):

	As of March 31,
	2018			2019
Balance as of the beginning of period	$	4,514		$	4,120
Amounts paid	(656		)	(751		)
Other adjustments to fair value	698			762
Balance at end of period	$	4,556		$	4,131