Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Summary of Fair Value Measurements of Cash Equivalents, Available-for-Sale Securities and Contingent Consideration Liability

The fair value measurements of cash equivalents, available-for-sale securities and the contingent consideration liability are identified at the following levels within the fair value hierarchy (in thousands):

	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		—

	December 31, 2016
	Fair Value Measurements
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents:
Money market funds	$	18,992	$	18,992	$	—	$	—
Total		18,992		18,992		—		—
Marketable securities:
Commercial paper securities		23,185		—		23,185		—
Corporate debt securities		10,004		—		10,004		—
U.S. government-sponsored entity debt securities		87,285		—		87,285		—
Total		120,474		—		120,474		—
Total cash equivalents and marketable securities	$	139,466	$	18,992	$	120,474	$	—