Composition of Total Revenue - Schedule of Net Product Sales by Geography (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Sales Information [Line Items]
Product sales, net	$ 128,596	$ 136,851	$ 186,537
ZEVALIN [Member]
Sales Information [Line Items]
Product sales, net	10,730	17,457	22,169
United States [Member]
Sales Information [Line Items]
Product sales, net	125,074	130,432	177,979
Total International [Member]
Sales Information [Line Items]
Product sales, net	3,522	6,419	8,558
Total International [Member] | Europe [Member] | ZEVALIN [Member]
Sales Information [Line Items]
Product sales, net	3,522	2,234	3,357
Total International [Member] | Asia Pacific [Member] | ZEVALIN [Member]
Sales Information [Line Items]
Product sales, net	$ 0	$ 4,185	$ 5,201
Geographic Concentration Risk [Member] | Sales [Member]
Sales Information [Line Items]
Percentage of sales	100.00%	100.00%	100.00%
Geographic Concentration Risk [Member] | Sales [Member] | United States [Member]
Sales Information [Line Items]
Percentage of sales	97.30%	95.30%	95.40%
Geographic Concentration Risk [Member] | Sales [Member] | Total International [Member]
Sales Information [Line Items]
Percentage of sales	2.70%	4.70%	4.60%
Geographic Concentration Risk [Member] | Sales [Member] | Total International [Member] | Europe [Member] | ZEVALIN [Member]
Sales Information [Line Items]
Percentage of sales	2.70%	1.60%	1.80%
Geographic Concentration Risk [Member] | Sales [Member] | Total International [Member] | Asia Pacific [Member] | ZEVALIN [Member]
Sales Information [Line Items]
Percentage of sales	0.00%	3.10%	2.80%