Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Additional Information (Detail)

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Commitments and Contingencies - Additional Information (Detail)
1 Months Ended 3 Months Ended 4 Months Ended 6 Months Ended
Aug. 01, 2015
ft²
Apr. 24, 2015
USD ($)
Aug. 31, 2016
USD ($)
Feb. 28, 2015
USD ($)
ft²
Jun. 30, 2017
USD ($)
Jun. 30, 2016
USD ($)
Apr. 24, 2015
USD ($)
Jun. 30, 2017
USD ($)
Jun. 30, 2016
USD ($)
Jun. 30, 2017
CAD
May 14, 2015
Feb. 01, 2015
USD ($)
Other Commitments [Line Items]                        
Expiration of operating lease agreement               2018-09        
Consolidated rent and facilities expense         $ 100,000 $ 100,000   $ 300,000 $ 300,000      
Indemnification obligations         0     0        
Expenses related to indemnification issues               0        
Ionis Pharmaceuticals Inc. [Member]                        
Other Commitments [Line Items]                        
Litigation settlement, upfront payment     $ 1,400,000                  
Royalty payment percentage     5.00%                  
Sale, license or other transaction payment percentage     50.00%                  
Ionis Pharmaceuticals Inc. [Member] | Maximum [Member]                        
Other Commitments [Line Items]                        
Litigation settlement, success based payment     $ 5,000,000                  
Grosvenor International Limited [Member]                        
Other Commitments [Line Items]                        
Area of office space leased | ft²       11,526                
Expiration date of option to lease additional area of office space       Aug. 01, 2015                
Lease expiration date       Apr. 30, 2018                
Optional lease renewal       3 years                
Monthly base rent commencement date       May 01, 2015                
Lessee's share of property tax percentage.       17.00%                
Construction allowance received for leasehold improvements                       $ 100,000
Deposit amount under lease agreement                       $ 200,000
Additional office space | ft² 2,245                      
Grosvenor International Limited [Member] | Maximum [Member]                        
Other Commitments [Line Items]                        
Monthly base rent       $ 20,000                
Grosvenor International Limited [Member] | Minimum [Member]                        
Other Commitments [Line Items]                        
Monthly base rent       $ 18,000                
BMR-217TH Place LLC [Member]                        
Other Commitments [Line Items]                        
Lease termination agreement, date of termination       Mar. 01, 2015                
Letter of credit drawn to pay deferred state sales tax       $ 100,000                
Letter of credit terminated       200,000                
Terminated lease       500,000                
Lease termination agreement, additional fee payable       1,300,000                
BMR-217TH Place LLC [Member] | Termination Fee [Member]                        
Other Commitments [Line Items]                        
Lease termination agreement, fee payable       2,000,000                
BMR-217TH Place LLC [Member] | Minimum [Member]                        
Other Commitments [Line Items]                        
Amount of funding to raise that would trigger payment of additional termination fee       $ 20,000,000                
Collaborative Arrangement [Member] | Teva Pharmaceutical Industries Ltd. [Member]                        
Other Commitments [Line Items]                        
Proceeds from advance reimbursement research and development             $ 27,000,000          
Hold-back amount and third-party expenses deducted from advanced reimbursement payment   $ 3,800,000         3,800,000          
Hold-back amount deducted from advanced reimbursement payment   3,000,000         3,000,000          
Third-party expenses deducted from advanced reimbursement payment             $ 800,000          
Maximum cost exposure if third-party agreements discovered after the termination date               $ 100,000        
Collaborative Arrangement [Member] | Ionis Pharmaceuticals Inc. [Member]                        
Other Commitments [Line Items]                        
Collaboration agreement aggregate amount   $ 23,200,000                    
Hold-back amount, requested payment percentage                     30.00%  
Lawsuit filing date               January 2016        
Range of each product line               10 years        
Collaborative Arrangement [Member] | Ionis Pharmaceuticals Inc. [Member] | Maximum [Member]                        
Other Commitments [Line Items]                        
Milestone payments         $ 4,300,000     $ 4,300,000        
Collaborative Arrangement [Member] | University of British Columbia [Member] | Maximum [Member]                        
Other Commitments [Line Items]                        
Milestone payments | CAD                   CAD 800,000    
Payments for royalty               $ 0