Financial Instruments - Summary of Money Market Funds and Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 22,895	$ 26,002
Unrealized Gain	1	2
Unrealized Loss	(4)	(16)
Estimated Fair Value	22,892	25,988
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	693	81
Estimated Fair Value	693	81
Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	150	250
Estimated Fair Value	150	250
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,947	898
Estimated Fair Value	4,947	898
Corporate debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,644	5,215
Unrealized Gain		1
Unrealized Loss	(1)	(5)
Estimated Fair Value	2,643	5,211
U.S. Government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,461	19,558
Unrealized Gain	1	1
Unrealized Loss	(3)	(11)
Estimated Fair Value	14,459	19,548
Cash and cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,142	281
Estimated Fair Value	3,142	281
Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,603	25,471
Unrealized Gain	1	2
Unrealized Loss	(4)	(16)
Estimated Fair Value	19,600	25,457
Long-term restricted investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	150	250
Estimated Fair Value	$ 150	$ 250