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Stockholders Equity - Additional Information (Detail) - USD ($) shares in Millions | 3 Months Ended
--- | ---
Mar. 31, 2016 | Mar. 31, 2015
Stockholders Equity Note [Line Items] |  |
Proceeds from common stock sold | $ 7,199,000 | $ 75,527,000
Cantor | Sales Agreement |  |
Stockholders Equity Note [Line Items] |  |
Maximum common stock offering price | $ 70,000,000 |
Percentage of proceeds payable as compensation to underwriter | 2.00% |
Common stock, number of shares issued | 1.2 |
Proceeds from common stock sold | $ 7,100,000 |
Common stock registered for sale | $ 15,300,000 |

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