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)
$ in Thousands
 3 Months Ended
Dec. 21, 2016
USD ($)
Mar. 31, 2018
USD ($)
Agreement
Dec. 31, 2017
USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]      
Unearned revenue recognized under units-of-revenue method – current   $ 658 $ 615 [1]
Unearned revenue recognized under units-of-revenue method – non-current   $ 17,019 17,123 [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  
Revenue recognized under units-of-revenue method   100  
Unearned revenue recognized under units-of-revenue method – current   700 600
Unearned revenue recognized under units-of-revenue method – non-current   17,000 $ 17,100
HCRP [Member] | First Acquisition Agreement [Member]      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]      
Upfront cash payment received $ 6,500    
Eligible potential additional payments receivable upon achievement of specified net sales milestones in future years 4,000 $ 3,000  
HCRP [Member] | Second Acquisition Agreement [Member]      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]      
Upfront cash payment received $ 11,500    
[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.