Equity Transactions - Summary of Common Stock Reserved for Issuance (Detail) shares in Thousands	Dec. 31, 2018 shares
Class of Stock [Line Items]
Total common stock reserved (in shares)	19,398
Series O Preferred Stock
Class of Stock [Line Items]
Total common stock reserved (in shares)	8,383
Common stock purchase warrants
Class of Stock [Line Items]
Total common stock reserved (in shares)	514
Options | Chief Executive Officer
Class of Stock [Line Items]
Total common stock reserved (in shares)	1,120
Equity incentive plans
Class of Stock [Line Items]
Total common stock reserved (in shares)	9,203
Employee stock purchase plan
Class of Stock [Line Items]
Total common stock reserved (in shares)	178