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Stockholders' Equity - Additional Information (Detail) - USD ($) |  |  |  |  |  |  |  |  | 1 Months Ended | 2 Months Ended | 6 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 13, 2017 | Jul. 13, 2016 | Jan. 12, 2016 | Dec. 04, 2015 | Apr. 10, 2015 | Mar. 18, 2015 | Nov. 18, 2014 | May 24, 2013 | Apr. 10, 2015 | Feb. 28, 2017 | Jun. 30, 2017 | Jun. 30, 2016 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Feb. 06, 2017 | Jul. 29, 2016 | May 10, 2016 | May 08, 2013
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares authorized |  |  |  |  |  |  |  |  |  |  | 5,000,000 |  | 5,000,000 | 5,000,000 |  |  |  |  |
Preferred stock, par value (usd per share) |  |  |  |  |  |  |  |  |  |  | $ 0.0001 |  | $ 0.0001 | $ 0.0001 |  |  |  |  |
Common stock, shares authorized |  |  |  |  |  |  |  |  |  |  | 350,000,000 |  | 350,000,000 | 275,000,000 |  |  |  |  |
Common stock, par value (usd per share) |  |  |  |  |  |  |  |  |  |  | $ 0.0001 |  | $ 0.0001 | $ 0.0001 |  |  |  |  |
Proceeds from issuance of shares |  |  |  |  |  |  |  |  |  |  | $ 5,000 | $ 78,000 | $ 95,000 | $ 309,000 | $ 263,000 |  |  |  |
Issuance of common stock, shares |  |  | 988,636 |  |  |  |  |  |  | 3,541,077 |  |  |  |  |  |  |  |  |
Net proceeds from issuance of common stock |  |  |  |  |  |  |  |  |  |  | $ 15,524,000 | $ 20,189,000 | $ 33,534,000 | $ 47,416,000 | 10,704,000 |  |  |  |
Number of shares availabe from warrants |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9,109
Exercise price |  | $ 13.00 | $ 28.40 |  |  |  |  |  |  |  | $ 79.40 |  | $ 79.40 | $ 79.40 |  |  | $ 8.60 | $ 30.20 | $ 49.4
Proceeds from issuance of shares, net underwriting discounts, commissions and offering expenses |  |  | $ 20,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Price per unit |  |  | $ 22.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock, value |  |  | $ 21,800,000 |  |  |  |  |  |  | $ 3,950,000 |  |  | $ 33,534,000 | $ 47,416,000 | $ 10,705,000 |  |  |  |
Number of securities called by each warrant |  |  | 0.60 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise period of warrants |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period from issuance which warrants is exercisable |  | 6 months 1 day |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of warrants |  | $ 11,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock, shares |  | 1,400,000 |  |  |  |  |  |  |  |  |  |  | 2,872,803 | 1,607,934 | 331,650 |  |  |  |
Price per unit |  | $ 9.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock, value |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 | $ 3,000 | $ 1,000 |  |  |  |
New warrants issued during period (in shares) |  | 700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lincoln Park Capital, LLC Purchase Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of shares |  |  |  |  |  |  | $ 4,900,000 |  |  |  |  |  |  |  | $ 8,500,000 |  |  |  |
Purchase agreement term |  |  |  |  |  |  | 36 months |  |  |  |  |  |  |  |  |  |  |  |
Stock issued during period related to purchase of assets |  |  |  |  |  |  | 125,000 |  |  |  |  |  |  |  |  |  |  |  |
Share price |  |  |  |  |  |  | $ 40.00 |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock, shares |  |  |  |  |  |  |  |  |  |  |  |  | 150,000 | 135,000 | 230,000 |  |  |  |
Net proceeds from issuance of common stock |  |  |  |  |  |  |  |  |  |  |  |  | $ 800,000 | $ 4,400,000 |  |  |  |  |
Remaining authorized repurchase amount |  |  |  |  |  |  |  |  |  |  | $ 2,000,000 |  |  |  |  | $ 2,100,000 |  |  |
Lincoln Park Capital, LLC Purchase Agreement | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares authorized under purchase agreement, shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 55,000,000 |  |  |
Authorized amount in stock repurchase program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 55,000,000 |  |  |
Lincoln Park Capital, LLC Purchase Agreement | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares authorized under purchase agreement, shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 15,600,000 |  |  |
Authorized amount in stock repurchase program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 15,600,000 |  |  |
Lincoln Park Capital, LLC Purchase Agreement | Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of shares |  |  |  |  |  |  | $ 50,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock, shares |  |  |  |  |  |  | 31,561 |  |  |  |  |  |  |  |  |  |  |  |
MLV & Co. LLC and Maxim Group LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 900,000 | $ 2,300,000 | $ 2,300,000 |  |  |  |
Issuance of common stock, shares |  |  |  |  |  |  |  |  |  |  |  |  | 334,000 | 72,000 | 70,000 |  |  |  |
Percent of gross proceeds |  |  |  |  |  |  |  | 3.00% |  |  |  |  |  |  |  |  |  |  |
At Market Issuance Sales Agreements, Maximum Gross Proceeds |  |  |  | $ 20,000,000 |  |  |  | $ 20,000,000 |  |  |  |  |  |  |  |  |  |  |
Remaining authorized repurchase amount |  |  |  | $ 19,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Underwritten Public Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares authorized |  |  |  |  |  | 182,692 |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of shares |  |  |  |  |  | $ 38,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Share price |  |  |  |  |  | $ 31.20 |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock, shares |  |  |  |  |  | 1,217,948 |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares availabe from warrants |  |  |  |  |  | 0.50 |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price |  |  |  |  |  | $ 41.60 |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued, overallotment option |  |  |  |  |  | 91,346 |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of shares, net underwriting discounts, commissions and offering expenses |  |  |  |  | $ 5,400,000 |  |  |  | $ 40,800,000 |  |  |  |  |  |  |  |  |  |
Underwritten Public Offering | Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock, shares | 17,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price | $ 1.10 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of shares, net underwriting discounts, commissions and offering expenses | $ 15,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Price per unit | $ 1.00 |  | $ 1.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
New warrants issued during period (in shares) | 17,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Warrant Or Right, Issued, Fair Value | $ 10,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over-Allotment Option |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares availabe from warrants |  |  | 88,977 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock available for issuance under warrants |  |  | 148,295 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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- Definition Amount remaining of a stock repurchase plan authorized. + References No definition available. + Details
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