Organization - Additional Information (Detail) - USD ($) $ in Thousands	Feb. 24, 2021	Dec. 31, 2020	Feb. 24, 2020	Dec. 31, 2019	Dec. 31, 2017	Apr. 26, 2006
Cash and cash equivalents		$ 115,069		$ 79,741
Accumulated deficit		$ (764,101)		$ (684,125)	$ (712,442)
Common stock, shares authorized		250,000,000		250,000,000		250,000,000
Common stock, shares outstanding		214,591,906		181,803,320
Common stock reserved for future issuance	31,115,329
Common Stock
Common stock, shares authorized			250,000,000
Common stock, shares outstanding	214,667,023		214,667,023
Common stock reserved for future issuance			31,115,329