Share-Based Payments - Summary of Restricted Stock Award Activity (Detail) - Restricted Stock - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of Shares
Outstanding at beginning of period (in shares)	2,950,782	981,208	196,453
Awarded (in shares)	3,389,455	2,164,374	981,208
Released (in shares)	(692,464)	(194,800)	(187,224)
Forfeited (in shares)	(54,704)	0	(9,229)
Outstanding at end of period (in shares)	5,593,069	2,950,782	981,208
Weighted Average Grant Fair Value
Outstanding at beginning of period (in dollars per share)	$ 2.41	$ 4.12	$ 7.01
Awarded (in dollars per share)	1.07	1.88	5.15
Released (in dollars per share)	2.49	5.14	7.05
Forfeited (in dollars per share)	1.47	0.00	6.32
Outstanding at end of period (in dollars per share)	$ 1.60	$ 2.41	$ 4.12