Debt - Long-Term Debt from Royalty-Bearing Instrument-December 2012 Financing - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 06, 2012	May 31, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Debt Disclosure [Line Items]
Long-term debt from royalty-bearing instrument, carrying amount net of unamortized discount			$ 73,732,000		$ 79,710,000
Interest expense, non-cash			446,000	$ 573,000
CPPIB
Debt Disclosure [Line Items]
Maximum repayment of future revenue and receivables			80,900,000
Repayment under agreement			$ 7,700,000
CPPIB | Scenario Forecast
Debt Disclosure [Line Items]
Repayment under agreement		$ 7,300,000
CPPIB | Vascepa
Debt Disclosure [Line Items]
Debt and future repayments percentage of net revenues			10.00%
BioPharma Debt
Debt Disclosure [Line Items]
Amount received at the closing of the agreement	$ 100,000,000
Maximum repayment of future revenue and receivables	150,000,000
Royalty-Bearing Debt
Debt Disclosure [Line Items]
Fair value of embedded derivative liability	$ 14,600,000
Gain (loss) on change in fair value of derivative liabilities			$ 0	$ 0
Long-term debt from royalty-bearing instrument, carrying amount net of unamortized discount			73,700,000		79,700,000
Royalty-Bearing Debt | Cash
Debt Disclosure [Line Items]
Interest expense, contractual coupon interest			1,200,000		1,500,000
Royalty-Bearing Debt | Non Cash
Debt Disclosure [Line Items]
Interest expense, non-cash			$ 400,000		$ 500,000