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Debt - Additional Information (Details)
$ / shares in Units, shares in Millions
1 Months Ended 9 Months Ended
May 01, 2020
USD ($)
$ / shares
shares
Apr. 23, 2020
USD ($)
Aug. 31, 2018
USD ($)
day
$ / shares
shares
Sep. 30, 2020
USD ($)
$ / shares
Sep. 30, 2019
USD ($)
May 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Debt Instrument [Line Items]              
Proceeds from convertible debt       $ 222,799,000 $ 0    
Convertible Debt              
Debt Instrument [Line Items]              
Carrying amount of equity component       99,026,000     $ 99,026,000
Debt issuance costs, net       $ 8,569,000      
Convertible Debt | Debt Covenant One              
Debt Instrument [Line Items]              
Threshold trading days | day     20        
Threshold consecutive trading days | day     30        
Threshold percentage of stock price trigger     130.00%        
Convertible Debt | Debt Covenant Two              
Debt Instrument [Line Items]              
Threshold trading days | day     5        
Threshold percentage of stock price trigger     98.00%        
Convertible Debt | Debt Covenant Three              
Debt Instrument [Line Items]              
Threshold percentage of stock price trigger     130.00%        
Redemption price, percentage     100.00%        
2023 Notes              
Debt Instrument [Line Items]              
Strike price (in dollars per share) | $ / shares       $ 41.59      
Equity component of convertible debt, subsequent adjustments     $ 26,910,000        
2023 Notes | Call Option              
Debt Instrument [Line Items]              
Strike price (in dollars per share) | $ / shares     $ 41.59        
Cap price (in dollars per share) | $ / shares     $ 63.98        
Option indexed to issuer's equity (in shares) | shares     5.5        
Equity component of convertible debt, subsequent adjustments     $ 26,900,000        
2023 Notes | Convertible Debt              
Debt Instrument [Line Items]              
Face amount     $ 230,000,000.0        
Interest rate     1.25% 1.25%      
Proceeds from convertible debt     $ 223,100,000        
Carrying amount of equity component     53,800,000 $ 52,194,000     52,194,000
Debt issuance costs, net     6,900,000 $ 3,274,000     4,032,000
Liability component     5,300,000        
Issuance costs of equity component     $ 1,600,000        
Converted instrument, rate     7.36%        
2023 Notes | Convertible Debt | Call Option              
Debt Instrument [Line Items]              
Option indexed to issuer's equity (in shares) | shares     5.5        
2023 Notes | Convertible Debt | Debt Covenant Three              
Debt Instrument [Line Items]              
Threshold trading days | day     20        
Threshold consecutive trading days | day     30        
Redemption price, percentage     100.00%        
2025 Notes              
Debt Instrument [Line Items]              
Strike price (in dollars per share) | $ / shares       $ 61.02      
Equity component of convertible debt, subsequent adjustments $ 27,255,000            
2025 Notes | Call Option              
Debt Instrument [Line Items]              
Strike price (in dollars per share) | $ / shares $ 61.02            
Cap price (in dollars per share) | $ / shares $ 93.88            
Option indexed to issuer's equity (in shares) | shares 3.8            
Equity component of convertible debt, subsequent adjustments $ 27,300,000            
2025 Notes | Convertible Debt              
Debt Instrument [Line Items]              
Face amount     $ 230,000,000.0        
Interest rate     2.25% 2.25%      
Proceeds from convertible debt     $ 222,800,000        
Carrying amount of equity component 48,300,000     $ 46,832,000     $ 46,832,000
Debt issuance costs, net 7,200,000     5,295,000      
Liability component 5,700,000            
Issuance costs of equity component $ 1,500,000            
Converted instrument, rate     7.85%        
2025 Notes | Convertible Debt | Call Option              
Debt Instrument [Line Items]              
Option indexed to issuer's equity (in shares) | shares     3.8        
Credit Agreement              
Debt Instrument [Line Items]              
Long-term line of credit       $ 0      
Credit Agreement | Revolving Credit Facility              
Debt Instrument [Line Items]              
Current borrowing capacity   $ 30,000,000.0       $ 50,000,000.0  
Credit sublimit   15,000,000.0          
Fee amount   $ 400,000          
Commitment fee percentage   0.20%          
Credit Agreement | Letter of Credit              
Debt Instrument [Line Items]              
Maximum borrowing capacity   $ 70,000,000.0          
Credit Agreement | London Interbank Offered Rate (LIBOR)              
Debt Instrument [Line Items]              
Basis spread on variable rate   2.50%          
Credit Agreement | London Interbank Offered Rate (LIBOR) | Minimum              
Debt Instrument [Line Items]              
Basis spread on variable rate   1.00%          
Credit Agreement | Base Rate              
Debt Instrument [Line Items]              
Basis spread on variable rate   0.00%