Cash, Cash Equivalents and Short-Term Investments and Long-Term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 43,413	$ 48,260
Unrealized Holdings Gains	2	1
Unrealized Holdings Losses	16	23
Fair Value	43,399	48,238
Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,197	27,043
Fair Value	19,197	27,043
Cash and Cash Equivalents | Cash
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,159	18,726
Fair Value	14,159	18,726
Cash and Cash Equivalents | Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,038	8,317
Fair Value	5,038	8,317
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,044	17,610
Unrealized Holdings Gains	2
Unrealized Holdings Losses	9	8
Fair Value	18,037	17,602
Short-term Investments | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,004	600
Unrealized Holdings Losses	3
Fair Value	1,001	600
Short-term Investments | U.S. treasury and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,300	6,432
Unrealized Holdings Losses		1
Fair Value	4,300	6,431
Short-term Investments | Corporate bonds and medium-term notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,252	8,586
Unrealized Holdings Gains	1
Unrealized Holdings Losses	5	6
Fair Value	6,248	8,580
Short-term Investments | Certificate of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,498
Unrealized Holdings Gains	1
Unrealized Holdings Losses	1
Fair Value	4,498
Short-term Investments | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,990	1,992
Unrealized Holdings Losses		1
Fair Value	1,990	1,991
Other Long-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,172	3,607
Unrealized Holdings Gains		1
Unrealized Holdings Losses	7	15
Fair Value	6,165	3,593
Other Long-term Investments | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		500
Unrealized Holdings Losses		4
Fair Value		496
Other Long-term Investments | U.S. treasury and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,596	597
Unrealized Holdings Gains		1
Unrealized Holdings Losses	4
Fair Value	2,592	598
Other Long-term Investments | Corporate bonds and medium-term notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,576	2,510
Unrealized Holdings Losses	3	11
Fair Value	$ 3,573	$ 2,499