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Debt (Narrative) (Detail)
$ / shares in Units, $ in Thousands
1 Months Ended 6 Months Ended
Nov. 30, 2015
USD ($)
Share
$ / shares
Dec. 31, 2017
USD ($)
Day
Debt Instrument [Line Items]    
Aggregate principal amount of notes $ 143,750  
Convertible Senior Notes due 2020 (the "Notes")    
Debt Instrument [Line Items]    
Aggregate principal amount of notes 125,000  
Aggregate principal amount of additional convertible debt 18,750  
Aggregate proceeds from convertible senior notes $ 143,750  
Debt interest rate 2.00%  
Number of common stock issue in conversion debt | Share 4,328  
Senior notes, initial conversion price per share | $ / shares $ 33.215  
Threshold multiple for debt conversion of notes   $ 1,000
Threshold trading days for convertible debt | Day   20
Threshold consecutive trading days for convertible debt | Day   30
Percentage of minimum stock price trigger for conversion   130.00%
Maximum calculated percentage to which trading price of notes is compared in order to trigger conversion feature of notes   98.00%