Nature of Business and Basis of Presentation - Additional Information (Detail) $ in Thousands			1 Months Ended		12 Months Ended
	Feb. 01, 2018 USD ($)	Jan. 20, 2017 USD ($)	Jan. 31, 2017 USD ($)	Jan. 31, 2012 USD ($)	Dec. 31, 2017 USD ($) Patient Employee Segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Nov. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	May 31, 2014 USD ($)
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					165
Number of operating segments | Segment					1
Total current assets					$ 153,270	$ 146,326
Cash and cash equivalents					$ 73,637	98,251	$ 106,961		$ 119,539
Net proceeds from public offering						64,613
Subsequent Event | American Depositary Shares
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Net proceeds from public offering	$ 65,000
Convertible Debt
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Convertible senior notes, stated interest rate					3.50%
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%
Convertible Debt | 2012 Notes
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Convertible senior notes, principal amount			$ 15,100	$ 150,000	$ 0	$ 15,100		$ 15,100		$ 31,300
Convertible senior notes, due date			2032	2032
Convertible senior notes, stated interest rate			3.50%	3.50%
Convertible senior notes, repurchase price at option of the issuer			100.00%	100.00%