Fair Value Measurement (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Measurement [Abstract]

Schedule of assets and liabilities measured at fair value on a recurring basis

Assets and liabilities measured at fair value on a recurring basis consist of the following as of September 30, 2018 (in thousands):

			Fair Value Measurements at Reporting Date Using
			Quoted Prices in		Significant
			Active Markets		Other		Significant
			for Identical		Observable		Unobservable
	September 30,		Assets/Liabilities		Inputs		Inputs
	2018		(Level 1)		(Level 2)		(Level 3)
Assets:
Money market funds	$	3,271	$	3,271	$	—	$	—
Marketable securities:
Corporate debt securities		41,465		—		41,465		—
Tax-exempt municipal securities		21,298		—		21,298		—
Variable rate demand notes		8,700		—		8,700		—
Total assets at fair value on a recurring basis	$	74,734	$	3,271	$	71,463	$	—
Liabilities:
Deferred payments	$	4,366	$	—	$	—	$	4,366

Assets and liabilities measured at fair value on a recurring basis consist of the following as of December 31, 2017 (in thousands):

			Fair Value Measurements at Reporting Date Using
			Quoted Prices in		Significant
			Active Markets		Other		Significant
			for Identical		Observable		Unobservable
	December 31,		Assets/Liabilities		Inputs		Inputs
	2017		(Level 1)		(Level 2)		(Level 3)
Assets:
Money market funds	$	113	$	113	$	—	$	—
Liabilities:
Deferred payments	$	4,514	$	—	$	—	$	4,514

Schedule of changes in fair value of level 3 liability

Changes in the fair value of the Company’s Level 3 liabilities during the nine months ended September 30, 2017 and 2018 are as follows (in thousands):

	September 30, 2017		September 30, 2018
Balance as of the beginning of period	$	11,741	$	4,514
Amounts paid		(1,133)		(1,412)
Other adjustments to fair value		(6,184)		1,264
Balance at end of period	$	4,424	$	4,366