Nature of Business and Basis of Presentation - Additional Information (Detail) $ in Thousands		3 Months Ended
Jan. 20, 2017 USD ($)	Mar. 31, 2018 USD ($) Patient Employee Segment	Dec. 31, 2017 USD ($)
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
REDUCE-IT study, number of patients enrolled and randomized \| Patient		8,175
Number of sales professionals \| Employee		170
Number of operating segments \| Segment		1
Total current assets		$ 207,551	$ 153,270
Cash and cash equivalents		129,049	$ 73,637
Convertible Debt \| 2017 Notes
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Convertible senior notes, principal amount	$ 30,000	$ 30,000
Convertible senior notes, due date	2047
Convertible senior notes, stated interest rate	3.50%
Convertible senior notes, repurchase price at option of the issuer	100.00%

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