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CONVERTIBLE SENIOR NOTES AND CAPPED CALL - Narrative (Details)
$ / shares in Units, shares in Millions
1 Months Ended 12 Months Ended
Feb. 28, 2019
USD ($)
day
$ / shares
shares
Mar. 31, 2019
USD ($)
$ / shares
Mar. 31, 2018
$ / shares
Debt Instrument [Line Items]      
Common stock, par value per share (in dollars per share) | $ / shares   $ 0.001 $ 0.001
Payments for capped call transactions   $ (33,724,000)  
Convertible Debt | Convertible Senior Notes      
Debt Instrument [Line Items]      
Debt instrument, face value $ 287,500,000.0 $ 287,500,000  
Debt instrument, interest rate 0.50%    
Proceeds from issuance of debt $ 245,800,000    
Debt instrument, convertible, conversion ratio 0.0389484    
Common stock, par value per share (in dollars per share) | $ / shares $ 0.001    
Debt instrument, convertible, conversion price (in dollars per share) | $ / shares $ 25.68    
Debt instrument, convertible, threshold trading days | day 20    
Debt instrument, convertible, threshold consecutive trading days | day 30    
Debt instrument, convertible, threshold percentage of stock price trigger 130.00%    
Debt instrument, convertible, measurement period | day 5    
Debt instrument, convertible, threshold consecutive trading days preceding measurement period | day 10    
Debt instrument, threshold percentage of sales price per share 98.00%    
Debt instrument, redemption price, percentage 100.00%    
Conversion option $ 66,700,000    
Debt instrument, effective interest rate 6.50%    
Debt issuance costs, net $ 600,000    
Debt instrument, strike price per share (in dollars per share) | $ / shares $ 25.68    
Debt instrument, initial cap price per share (in dollars per share) | $ / shares $ 39.50    
Payments for capped call transactions $ 33,700,000    
Call Option | Convertible Debt | Convertible Senior Notes      
Debt Instrument [Line Items]      
Option indexed to issuer's equity, indexed shares (in shares) | shares 11.2