Investment in Silver Creek - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	9 Months Ended
	May 07, 2019	May 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Sep. 30, 2017
Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Effects Of Changes Net [Line Items]
Equity method investment					$ 7,428
Proceeds from maturities and sales of marketable securities			$ 51,500	$ 42,200
Equity method investment realized gain loss on sale			$ 1,400
Silver Creek Pharmaceuticals, Inc. [Member]
Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Effects Of Changes Net [Line Items]
Equity method investment	$ 6,400
Proceeds from maturities and sales of marketable securities	$ 7,800	$ 7,800
Silver Creek Pharmaceuticals, Inc. [Member] | Maximum [Member]
Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Effects Of Changes Net [Line Items]
Ownership interest percentage held by parent						50.00%