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Net Loss per Share - Additional Information (Detail) - 0.25% Convertible Senior Notes Due 2022 as Liability Component [Member]
3 Months Ended
Mar. 31, 2019
d
$ / shares
Earnings Per Share Basic [Line Items]  
Common stock conversion price | $ / shares $ 94.77
Debt instrument, convertible, threshold trading days 20
Debt instrument, convertible, threshold consecutive trading days 30
Percentage of closing price to trigger debt conversion 130.00%