Net Product Sales by Geographic Region and Product Line - Schedule of Product Sales, Net by Geography (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Sales Information [Line Items]
Product sales, net	$ 35,241	$ 38,413
Percentage of product sales, net	100.00%	100.00%
United States [Member]
Sales Information [Line Items]
Product sales, net	$ 33,779	$ 36,546
Percentage of product sales, net	95.90%	95.10%
Total International [Member]
Sales Information [Line Items]
Product sales, net	$ 1,462	$ 1,867
Percentage of product sales, net	4.10%	4.90%
Total International [Member] | Europe (ZEVALIN only) [Member]
Sales Information [Line Items]
Product sales, net	$ 1,462	$ 644
Percentage of product sales, net	4.10%	1.70%
Total International [Member] | Asia Pacific (ZEVALIN only)[Member]
Sales Information [Line Items]
Product sales, net	$ 0	$ 1,223
Percentage of product sales, net	0.00%	3.20%