Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Details)

v3.8.0.1
Fair Value Measurements (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
U.S treasury obligations    
Assets and liabilities measure at fair value on a recurring basis:    
Marketable securities $ 39,799 $ 25,005
Money market funds    
Assets and liabilities measure at fair value on a recurring basis:    
Cash and cash equivalents 12,149 58,588
Overnight repurchase agreements    
Assets and liabilities measure at fair value on a recurring basis:    
Cash and cash equivalents 30,000  
Recurring    
Assets and liabilities measure at fair value on a recurring basis:    
Total 81,948 83,593
Recurring | U.S treasury obligations    
Assets and liabilities measure at fair value on a recurring basis:    
Marketable securities 39,799 25,005
Recurring | Money market funds    
Assets and liabilities measure at fair value on a recurring basis:    
Cash and cash equivalents 12,149 58,588
Recurring | Overnight repurchase agreements    
Assets and liabilities measure at fair value on a recurring basis:    
Cash and cash equivalents 30,000  
Recurring | Level 1    
Assets and liabilities measure at fair value on a recurring basis:    
Total 51,948 83,593
Recurring | Level 1 | U.S treasury obligations    
Assets and liabilities measure at fair value on a recurring basis:    
Marketable securities 39,799 25,005
Recurring | Level 1 | Money market funds    
Assets and liabilities measure at fair value on a recurring basis:    
Cash and cash equivalents 12,149 $ 58,588
Recurring | Level 2    
Assets and liabilities measure at fair value on a recurring basis:    
Total 30,000  
Recurring | Level 2 | Overnight repurchase agreements    
Assets and liabilities measure at fair value on a recurring basis:    
Cash and cash equivalents $ 30,000