Quarterly report pursuant to Section 13 or 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
Mar. 31, 2019
Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]    
Cash and cash equivalents $ 39,844 $ 37,539
Marketable securities 11,079 13,565
Cash [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Cash and cash equivalents 19,224 13,337
Fair Value, Cash 19,224 13,337
Level 1 [Member] | Money Market Funds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Cash and cash equivalents 20,620 24,202
Cash and cash equivalents gross before unrealized losses 20,622 24,202
Gross Unrealized Losses (2)  
Fair Value, Cash 20,620 24,202
Level 2 [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Cash and cash equivalents 39,844 37,539
Marketable securities 11,079 13,565
Debt Securities   13,613
Gross Unrealized Losses (14) (48)
Fair Value, Debt Securities   13,565
Total Cash and Debt Securities 50,937 51,152
Total Fair Value, Cash and Debt Securities 50,923 51,104
Level 2 [Member] | U.S. Government Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Marketable securities   2,498
Debt Securities   2,500
Gross Unrealized Losses   (2)
Fair Value, Debt Securities   2,498
Level 2 [Member] | Corporate Debt Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Marketable securities 11,079 11,067
Debt Securities 11,091 11,113
Gross Unrealized Losses (12) (46)
Fair Value, Debt Securities $ 11,079 $ 11,067