Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Summary of Cash Equivalents, Marketable Securities and Long-Term Investments Measured at Fair Value

Cash equivalents, marketable securities and long-term investments measured at fair value are classified in the table below in one of the three categories described above (in thousands):

	Fair Value Measurements
December 31, 2017	Level 1		Level 2		Level 3		Total
Certificates of deposit	$	1,225	$	—	$	—	$	1,225
Money market funds		21,760		—		—		21,760
U.S. treasuries		34,433		—		—		34,433
Auction rate securities		—		—		2,209		2,209
	$	57,418	$	—	$	2,209	$	59,627

	Fair Value Measurements
December 31, 2016	Level 1		Level 2		Level 3		Total
Certificates of deposit	$	7,275	$	—	$	—	$	7,275
Money market funds		1,171		—		—		1,171
U.S. treasuries		23,277		—		—		23,277
Auction rate securities		—		—		2,046		2,046
	$	31,723	$	—	$	2,046	$	33,769

Summary of Activity for Assets Measured at Fair Value Using Significant Unobservable Inputs

Activity for assets measured at fair value using significant unobservable inputs (Level 3) is presented in the table below (in thousands):

Balance at December 31, 2016	$	2,046
Total net realized gains included in earnings		—
Total net unrealized gains included in other comprehensive income		163
Net transfers in and/out of Level 3		—
Balance at December 31, 2017	$	2,209
Amount of total losses for the period included in net loss attributable to the change in unrealized gains or losses  relating to assets still held at December 31, 2017	$	—