XML 54 R39.htm IDEA: XBRL DOCUMENT v3.8.0.1
Commitments and Contingencies - Additional Information (Detail) - USD ($)
1 Months Ended 12 Months Ended
Jan. 31, 2016
Oct. 31, 2014
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Caribou [Member]          
Operating Leased Assets [Line Items]          
Percentage of shares owned     10.70%    
Caribou [Member] | Maximum [Member] | Development And Regulatory Milestones [Member]          
Operating Leased Assets [Line Items]          
Milestone payments     $ 6,400,000    
Caribou [Member] | Maximum [Member] | Sales Based Milestones [Member]          
Operating Leased Assets [Line Items]          
Milestone payments     20,000,000    
Property Leases [Member]          
Operating Leased Assets [Line Items]          
Rent expense     6,000,000 $ 2,700,000 $ 600,000
Property Leases [Member] | Cambridge, Massachusetts [Member]          
Operating Leased Assets [Line Items]          
Operating lease security deposit $ 2,200,000 $ 300,000      
Capital lease obligation additional period of term of leases in years 3 years 5 years      
Operating lease arrangement term 10 years        
Number of lease years before optional extension and early termination can be exercised 6 years        
Prepaid lease payments     $ 3,300,000