Organization and Going Concern - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Nature Of Operations [Line Items]
Accumulated Deficit	$ (657,997)	$ (492,700)
Cash and cash equivalents	$ 81,053	$ 140,717	$ 42,803	$ 68,204