XML 43 R31.htm IDEA: XBRL DOCUMENT v3.19.2
Fair Value Measurements and Marketable Securities - Additional Information (Detail) - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2018
Mar. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]            
Total cash $ 4,200,000       $ 5,400,000  
Fair value assets level 1 to level 2 transfers 0          
Fair value assets level 2 to level 1 transfers 0          
Fair value liabilities level 1 to level 2 transfers 0          
Fair value liabilities level 2 to level 1 transfers 0          
Transfer of financial asset into level 3 of fair value 0          
Transfer of financial liabilities into level 3 of fair value 0          
Spero Gyrase, Inc. [Member] | Anti- dilution Rights [Member]            
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]            
Derivative liabilities $ 200,000 $ 200,000     $ 200,000 $ 1,600,000
Fair value inputs probability of funding     0.00% 100.00%    
Increase (decrease) derivative liabilities   $ (1,400,000)