Annual report pursuant to Section 13 and 15(d)

Financial Instruments - Schedule of Cash and Available-For-Sale Securities' Cost, Gross Unrealized Losses and Fair Value by Significant Investment Category (Detail)

v3.19.1
Financial Instruments - Schedule of Cash and Available-For-Sale Securities' Cost, Gross Unrealized Losses and Fair Value by Significant Investment Category (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]      
Cash and cash equivalents $ 37,539 $ 29,545 $ 12,078
Marketable securities 13,565 39,598  
Cash [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Cash and cash equivalents 13,337 8,925  
Fair Value, Cash 13,337 8,925  
Level 1 [Member] | Money Market Funds [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Cash and cash equivalents 24,202 20,620  
Fair Value, Cash 24,202 20,620  
Level 2 [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Cash and cash equivalents 37,539 29,545  
Marketable securities 13,565 39,598  
Debt Securities 13,613 39,732  
Gross Unrealized Losses (48) (134)  
Fair Value, Debt Securities 13,565 39,598  
Total Cash and Debt Securities 51,152 69,277  
Total Fair Value, Cash and Debt Securities 51,104 69,143  
Level 2 [Member] | U.S. Government Securities [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Marketable securities 2,498 4,488  
Debt Securities 2,500 4,505  
Gross Unrealized Losses (2) (17)  
Fair Value, Debt Securities 2,498 4,488  
Level 2 [Member] | Corporate Debt Securities [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Marketable securities 11,067 30,156  
Debt Securities 11,113 30,268  
Gross Unrealized Losses (46) (112)  
Fair Value, Debt Securities $ 11,067 30,156  
Level 2 [Member] | Commercial Papers [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Marketable securities   4,954  
Debt Securities   4,959  
Gross Unrealized Losses   (5)  
Fair Value, Debt Securities   $ 4,954