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Convertible Senior Notes - Additional Information (Detail)
3 Months Ended 12 Months Ended
May 24, 2016
USD ($)
D
$ / shares
Dec. 31, 2018
USD ($)
D
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Debt Instrument [Line Items]          
Proceeds from issuance of convertible senior notes, net of costs       $ 111,070,000
Accretion of the debt discount     $ 4,248,000 $ 3,977,000 $ 2,274,000
2.125% Convertible Senior Notes due 2021          
Debt Instrument [Line Items]          
Notes issued $ 115,000,000     11,000  
Notes, interest rate 2.125% 2.125% 2.125%    
Proceeds from issuance of convertible senior notes, net of costs $ 111,100,000        
Notes, frequency of periodic payment     Semi-annually    
Notes, date of first required payment     Dec. 01, 2016    
Notes, due date     Jun. 01, 2021    
Loss on conversion of senior convertible notes     $ (1,000)    
Notes threshold percentage of stock price trigger   130.00%      
Notes threshold trading days | D   20      
Notes threshold consecutive trading days | D   30      
Debt instrument, convertible if-converted value in excess of principal     69,600,000    
Notes conversion ratio per $1,000 principal amount 31.1813        
Notes initial conversion price | $ / shares $ 32.07        
Debt covenants debt default holder percent to declare all notes due minimum 25.00%        
Number of days within which entity fails to satisfy obligations considered as event of default 270 days        
Notes issued, fair value $ 96,300        
Contractual coupon interest     2,400 2,400  
Accretion of the debt discount     3,600 3,400  
Amortization of the debt issuance costs     $ 600 600  
Effective interest rate on the Notes   6.60% 6.60%    
Notes, carrying value   $ 103,488,000 $ 103,488,000 $ 99,250,000  
Fair value of the note   $ 184,600,000 $ 184,600,000    
2.125% Convertible Senior Notes due 2021 | On any business day on or after June 5, 2019 and prior to the maturity date          
Debt Instrument [Line Items]          
Notes threshold percentage of stock price trigger 130.00%        
Notes threshold trading days | D 20        
Notes threshold consecutive trading days | D 30        
Notes redemption price 100.00%