Background - Additional Information (Detail) $ in Thousands |
1 Months Ended | 12 Months Ended | ||||
|---|---|---|---|---|---|---|
|
Feb. 28, 2017
USD ($)
|
Jan. 31, 2014
USD ($)
|
Dec. 31, 2016
USD ($)
Segment
|
Dec. 31, 2015
USD ($)
|
Dec. 31, 2014
USD ($)
|
Dec. 31, 2013
USD ($)
|
|
| Accounting Policies and General Information [Line Items] | ||||||
| Number of business segments | Segment | 1 | |||||
| Accumulated deficit | $ (318,279) | $ (302,942) | ||||
| Cash and cash equivalents | $ 14,753 | $ 23,027 | $ 26,127 | $ 31,948 | ||
| Proceeds from common stock issued in public offerings | $ 18,800 | |||||
| Subsequent Event [Member] | ||||||
| Accounting Policies and General Information [Line Items] | ||||||
| Proceeds from common stock issued in public offerings | $ 20,900 | |||||