Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Company's Available-for-Sale Securities by Level within Fair Value Hierarchy

The Company’s available-for-sale securities by level within the fair value hierarchy were as follows (in thousands):

Type of securities as of December 31, 2017	Fair value measurement using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market fund	$	22,398	$	—	$	—	$	22,398
Short-term investments:
Corporate debt securities	—		35,514		—		35,514
U.S. government-related debt securities	—		15,905		—		15,905
Total	$	22,398	$	51,419	$	—	$	73,817

Type of securities as of December 31, 2016	Fair value measurement using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market fund	$	16,715	$	—	$	—	$	16,715
Short-term investments:
Corporate debt securities	—		36,160		—		36,160
U.S. government-related debt securities	—		17,293		—		17,293
Total	$	16,715	$	53,453	$	—	$	70,168