Fair Value Measurement (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Summary of Fair Value Measurements of Cash Equivalents, and Available-for-Sale Marketable Securities

The fair value measurements of the Company’s cash equivalents and available-for-sale marketable securities are identified at the following levels within the fair value hierarchy (in thousands):

	September 30, 2018
	Fair Value Measurements
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents:
Money market funds	$	18	$	18	$	—	$	—
Total		18		18		—		—
Marketable securities:
Commercial paper securities		317,119		—		317,119		—
Corporate debt securities		83,579		—		83,579		—
U.S. government-sponsored entity debt securities		18,574		—		18,574		—
Total		419,272		—		419,272		—
Total cash equivalents and marketable securities	$	419,290	$	18	$	419,272		—

	December 31, 2017
	Fair Value Measurements
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents:
Money market funds	$	24,290	$	24,290	$	—	$	—
Commercial paper securities		4,595		—		4,595		—
Total		28,885		24,290		4,595		—
Marketable securities:
Commercial paper securities		110,247		—		110,247		—
Corporate debt securities		75,755		—		75,755		—
U.S. government-sponsored entity debt securities		8,492		—		8,492		—
Total		194,494		—		194,494		—
Total cash equivalents and marketable securities	$	223,379	$	24,290	$	199,089		—