Annual report pursuant to Section 13 and 15(d)

Schedule of Changes in Common Stock Outstanding (Parenthetical) (Detail)

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Schedule of Changes in Common Stock Outstanding (Parenthetical) (Detail) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 12 Months Ended
Jun. 30, 2016
May 31, 2016
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Class of Stock [Line Items]          
Offering price of common stock   $ 5.25     $ 12.50
Issuance of common stock, net of issuance fees   $ 15,200 $ 16,192 $ 8,960 $ 8,614
Issuance of common stock in a private placement $ 1,000   $ 1,000