Quarterly report pursuant to Section 13 or 15(d)

Licensing and Other Arrangements - Sale of Future Revenue Streams - Additional Information (Details)

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Licensing and Other Arrangements - Sale of Future Revenue Streams - Additional Information (Details)
 3 Months Ended 6 Months Ended
Dec. 21, 2016
USD ($)
Jun. 30, 2018
USD ($)
Jun. 30, 2017
USD ($)
Jun. 30, 2018
USD ($)
Agreement
Jun. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]            
Unearned revenue recognized under units-of-revenue method – current   $ 171,000   $ 171,000   $ 615,000 [1]
Unearned revenue recognized under units-of-revenue method – non-current   17,592,000   $ 17,592,000   17,123,000 [1]
HCRP [Member]            
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]            
Number of royalty Interest acquisition agreements | Agreement       2    
Unearned revenue recognized under units-of-revenue method   18,000,000   $ 18,000,000    
Revenue recognized under units-of-revenue method   43,000 $ 100,000 197,000 $ 200,000  
Reversed revenue recognized under units-of-revenue method   129,000   222,000    
Decrease in net revenue due to change in estimate of product sales   (86,000)   (25,000)    
Unearned revenue recognized under units-of-revenue method – current   200,000   200,000   600,000
Unearned revenue recognized under units-of-revenue method – non-current   $ 17,600,000   17,600,000   $ 17,100,000
HCRP [Member] | First Acquisition Agreement [Member]            
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]            
Upfront cash payment received $ 6,500,000          
Eligible potential additional payments receivable upon achievement of specified net sales milestones in future years 4,000,000     $ 3,000,000    
HCRP [Member] | Second Acquisition Agreement [Member]            
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]            
Upfront cash payment received $ 11,500,000          
[1] The condensed consolidated balance sheet as of December 31, 2017 has been derived from the audited consolidated financial statements as of that date included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017.