Cash, Cash Equivalents and Investments - Short-term and Long-term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 500	$ 8,173
Gross Unrealized Losses		(27)
Estimated Fair Value	500	8,146
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	500	1,499
Gross Unrealized Losses		(6)
Estimated Fair Value	$ 500	1,493
US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,003
Gross Unrealized Losses		(4)
Estimated Fair Value		999
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		4,169
Gross Unrealized Losses		(14)
Estimated Fair Value		4,155
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,502
Gross Unrealized Losses		(3)
Estimated Fair Value		$ 1,499