Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Details)

v3.8.0.1
Fair Value Measurements (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
U.S treasury obligations    
Assets measured at fair value on a recurring basis:    
Marketable securities $ 39,844 $ 25,005
Money market funds    
Assets measured at fair value on a recurring basis:    
Cash and cash equivalents 17,205 58,588
Overnight repurchase agreements    
Assets measured at fair value on a recurring basis:    
Cash and cash equivalents 15  
Recurring    
Assets measured at fair value on a recurring basis:    
Total 72,049 83,593
Recurring | U.S treasury obligations    
Assets measured at fair value on a recurring basis:    
Marketable securities 39,844 25,005
Recurring | Money market funds    
Assets measured at fair value on a recurring basis:    
Cash and cash equivalents 17,205 58,588
Recurring | Overnight repurchase agreements    
Assets measured at fair value on a recurring basis:    
Cash and cash equivalents 15,000  
Recurring | Level 1    
Assets measured at fair value on a recurring basis:    
Total 57,049 83,593
Recurring | Level 1 | U.S treasury obligations    
Assets measured at fair value on a recurring basis:    
Marketable securities 39,844 25,005
Recurring | Level 1 | Money market funds    
Assets measured at fair value on a recurring basis:    
Cash and cash equivalents 17,205 $ 58,588
Recurring | Level 2    
Assets measured at fair value on a recurring basis:    
Total 15,000  
Recurring | Level 2 | Overnight repurchase agreements    
Assets measured at fair value on a recurring basis:    
Cash and cash equivalents $ 15,000