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Fair Value Measurements - Additional Information (Detail) - USD ($)
$ in Thousands, shares in Millions
1 Months Ended 6 Months Ended
Jun. 28, 2018
May 09, 2018
Oct. 31, 2015
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Debt Instrument [Line Items]            
Proceeds from issuance of convertible senior notes       $ 10,000 $ 0  
Proceeds from Issuance of Common Stock   $ 10,000   0 $ 73,125  
Convertible debt, fair value disclosures       $ 133,800   $ 155,400
Additional shares issued (in shares)   2.2        
Convertible Senior Notes, due 2020            
Debt Instrument [Line Items]            
Proceeds from issuance of convertible senior notes     $ 125,000      
Convertible Debt | Convertible Senior Notes due 2021            
Debt Instrument [Line Items]            
Senior notes issued   $ 164,746        
Additional shares issued (in shares) 4.0 4.0