Equity Investment - Additional Information (Detail) - USD ($) shares in Millions	1 Months Ended		3 Months Ended		12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Share of loss from equity method investee			$ 226,000	$ 70,000
PACT Pharma
Schedule of Equity Method Investments [Line Items]
Equity method investment agreement termination date					Dec. 31, 2018
Share of loss from equity method investee			200,000	70,000
Equity method investments impairment			0	$ 0
PACT Pharma | Variable interest entity
Schedule of Equity Method Investments [Line Items]
Receivable from PACT Pharma			$ 54,000			$ 25,000
PACT Pharma | Series A Preferred Stock
Schedule of Equity Method Investments [Line Items]
Purchase of common stock, shares	1.0
Purchase of common stock, value	$ 1,000,000
PACT Pharma | Common Stock
Schedule of Equity Method Investments [Line Items]
Purchase of common stock, shares		3.6