NET PRODUCT REVENUES - Summary of Net Product Revenues Of ONPATTRO (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 99,476	$ 33,294
Net product revenues
Disaggregation of Revenue [Line Items]
Total revenues	71,938	26,291
ONPATTRO
Disaggregation of Revenue [Line Items]
Total revenues	66,664	26,291
GIVLAARI
Disaggregation of Revenue [Line Items]
Total revenues	5,274	0
United States | Net product revenues
Disaggregation of Revenue [Line Items]
Total revenues	42,470	18,760
Europe | Net product revenues
Disaggregation of Revenue [Line Items]
Total revenues	21,166	7,531
Rest of World (primarily Japan) | Net product revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ 8,302	$ 0