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Financing Transactions - Additional Information (Detail) - USD ($)
6 Months Ended 12 Months Ended
Aug. 02, 2019
Oct. 16, 2017
May 02, 2017
Nov. 15, 2016
Jun. 07, 2016
Jun. 30, 2019
Dec. 31, 2019
Dec. 31, 2017
Dec. 31, 2018
Class Of Stock [Line Items]                  
Long-term debt, net             $ 40,176,000   $ 3,640,000
Net proceeds from follow-on public offering               $ 132,666,000  
Common stock, shares issued             38,361,476   37,946,341
Follow On Public Offering [Member]                  
Class Of Stock [Line Items]                  
Common stock, shares issued   5,520,000   4,140,000 5,900,000        
Sale of common stock price per share   $ 25.50   $ 18.00 $ 14.00        
Net proceeds from follow-on public offering   $ 132,200,000              
2015 Term Loan [Member]                  
Class Of Stock [Line Items]                  
Repayments of lines of credit             $ 7,700,000    
Silicon Valley Bank [Member] | Revolving Credit Facility [Member]                  
Class Of Stock [Line Items]                  
Debt instrument maturity date             Jan. 01, 2024    
Term loan, maximum borrowings $ 20,000,000.0                
Silicon Valley Bank [Member] | 2019 Term Loan [Member]                  
Class Of Stock [Line Items]                  
Term loan, principal amount 40,000,000.0                
Debt instrument maturity date             Jan. 01, 2024    
Long-term debt, net $ 40,000,000.0                
Debt instrument date of first required payment Feb. 01, 2021                
Silicon Valley Bank [Member] | 2015 Term Loan [Member]                  
Class Of Stock [Line Items]                  
Long-term debt, net $ 40,000,000.0           $ 40,000,000.0    
Silicon Valley Bank And MidCap Financial Funding XIII Trust [Member] | 2019 Term Loan [Member]                  
Class Of Stock [Line Items]                  
Repayments of lines of credit 7,700,000                
Silicon Valley Bank And MidCap Financial Funding XIII Trust [Member] | 2015 Term Loan [Member]                  
Class Of Stock [Line Items]                  
Repayments of lines of credit $ 7,700,000                
2024 Convertible Notes [Member]                  
Class Of Stock [Line Items]                  
Term loan, principal amount     $ 201,300,000       $ 201,300,000    
Debt instrument maturity date     May 01, 2024            
Debt instrument interest rate     3.375%       3.375%    
Debt instrument frequency of periodic payment           semi-annually semi-annually    
Debt instrument date of first required payment     Nov. 01, 2017            
Net proceeds from offering of convertible senior notes     $ 194,800,000            
Debt issuance costs     $ 6,500,000       $ 68,900,000