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Redeemable Convertible Preferred Shares - Additional Information (Detail) |  |  |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended
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Oct. 20, 2017 | Jul. 31, 2017 USD ($) $ / shares shares | Jun. 30, 2017 $ / shares shares | Mar. 31, 2017 USD ($) $ / shares shares | Jul. 31, 2017 USD ($) $ / shares shares | Jun. 30, 2017 $ / shares shares | Mar. 31, 2017 USD ($) $ / shares shares | Feb. 29, 2016 USD ($) $ / shares shares | Jul. 01, 2015 USD ($) $ / shares shares | Jun. 30, 2015 USD ($) $ / shares shares | Jan. 31, 2015 USD ($) $ / shares shares | Mar. 31, 2017 USD ($) $ / shares | Dec. 31, 2017 USD ($) Installment $ / shares | Dec. 31, 2016 USD ($) $ / shares shares | Dec. 31, 2015 USD ($) $ / shares shares
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion of bridge units in to preferred units |  |  |  |  |  |  |  |  |  |  |  | $ 8,500,000 | $ 8,500,000 |  | $ 8,000,000
Payment of offering costs |  |  |  |  |  |  |  |  |  |  |  |  | 3,574,000 |  |
Fair value of tranche right |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 909,000 | $ 2,401,000
Share conversion ratio |  |  | 1 |  |  | 1 |  |  |  |  |  |  |  |  |
Proceeds from issuance of preferred units |  |  |  |  |  |  |  |  |  |  |  |  | $ 50,000,000 |  |
Percentage of voting to be held by holders of senior preferred stock for deemed liquidation event |  |  |  |  |  |  |  |  |  |  |  |  | 60.00% |  |
Preferred stock dividend rate |  |  |  |  |  |  |  |  |  |  |  |  | 8.00% |  |
Dividends paid | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 | $ 0 |
Dividends declared | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 | 0 |
Redemption date of redeemable preferred stock |  |  |  |  |  |  |  |  |  |  |  |  | Feb. 01, 2021 |  |
Number of annual installments for redemption | Installment |  |  |  |  |  |  |  |  |  |  |  |  | 3 |  |
Preferred stock notice period for redemption |  |  |  |  |  |  |  |  |  |  |  |  | 60 days |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reverse stock split ratio | 0.164544 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reverse stock split | One-for-6.0774 |  |  |  |  |  |  |  |  |  |  |  |  |  |
2015 Bridge Units [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Bridge units issued and sold | shares |  |  |  |  |  |  |  |  |  |  | 8,000 |  |  |  |
Bridge units issued price per unit | $ / shares |  |  |  |  |  |  |  |  |  |  | $ 1,000 |  |  |  |
Conversion of bridge units in to preferred units |  |  |  |  |  |  |  |  |  |  | $ 8,000,000 |  |  |  |
Redeemable issuer option value |  |  |  |  |  |  |  |  |  |  | $ 2,300,000 |  |  |  |
2015 Bridge Units [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Bridge units discount percentage |  |  |  |  |  |  |  |  |  |  | 20.00% |  |  |  |
2015 Bridge Units [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Bridge units discount percentage |  |  |  |  |  |  |  |  |  |  | 25.00% |  |  |  |
Class A Preferred Unit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible shares, par value | $ / shares |  |  |  |  |  |  |  |  |  | $ 3.90 |  |  |  |  | $ 4.40
Conversion of bridge units in to preferred units |  |  |  |  |  |  |  |  | $ 8,000,000 |  |  |  |  |  |
Redeemable issuer option value |  |  |  |  |  |  |  |  | $ 900,000 |  |  |  |  |  |
Redeemable convertible shares issued and sold | shares |  |  |  |  |  |  |  |  | 2,279,202 | 1,923,076 |  |  |  |  | 3,295,455
Proceeds from issuance of preferred units, net of issuance costs |  |  |  |  |  |  |  |  |  | $ 7,300,000 |  |  |  |  | $ 14,500,000
Payment of offering costs |  |  |  |  |  |  |  |  |  | $ 200,000 |  |  |  |  |
Preferred units discount percentage |  |  |  |  |  |  |  |  | 10.00% | 20.00% |  |  |  |  |
Conversion price of redeemable preferred share | $ / shares |  |  |  |  |  |  |  |  | $ 3.51 | $ 3.90 |  |  |  |  |
Convertible debt fair value disclosures |  |  |  |  |  |  |  |  | $ 8,900,000 |  |  |  |  |  |
Liability fair value adjustment |  |  |  |  |  |  |  |  | 8,000,000 |  |  |  |  |  |
Gain on extinguishment |  |  |  |  |  |  |  |  | $ 0 |  |  |  |  |  |
Fair value of tranche right |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,400,000
Class B Preferred Unit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible shares, par value | $ / shares |  |  |  |  |  |  |  | $ 4.40 |  |  |  |  |  | $ 5.28 |
Redeemable convertible shares issued and sold | shares |  |  |  |  |  |  |  | 5,909,089 |  |  |  |  |  | 1,609,846 |
Proceeds from issuance of preferred units, net of issuance costs |  |  |  |  |  |  |  | $ 25,900,000 |  |  |  |  |  | $ 8,500,000 |
Payment of offering costs |  |  |  |  |  |  |  | $ 100,000 |  |  |  |  |  |  |
Fair value of tranche right |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 900,000 |
2016 Bridge Units [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Bridge units issued and sold | shares |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,500 |
Bridge units issued price per unit | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,000 |
Conversion of bridge units in to preferred units |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 8,500,000 |
Bridge units discount percentage |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% |
Redeemable issuer option value |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 900,000 |
Change in fair value |  |  |  |  |  |  |  |  |  |  |  |  |  | 300,000 |
Class C Preferred Units [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible shares, par value | $ / shares |  |  |  | $ 1.7749 |  |  | $ 1.7749 |  |  |  |  | $ 1.7749 |  |  |
Conversion of bridge units in to preferred units |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,500,000 |
Redeemable issuer option value |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 900,000 |
Redeemable convertible shares issued and sold | shares |  |  |  | 24,326,470 |  |  | 24,326,470 |  |  |  |  |  |  | 5,321,112 |
Proceeds from issuance of preferred units, net of issuance costs |  |  |  | $ 43,000,000 |  |  | $ 43,000,000 |  |  |  |  |  |  |  |
Payment of offering costs |  |  |  | $ 200,000 |  |  | $ 200,000 |  |  |  |  |  |  |  |
Preferred units discount percentage |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% |
Conversion price of redeemable preferred share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1.60 |
Convertible debt fair value disclosures |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 9,400,000 |
Liability fair value adjustment |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,500,000 |
Gain on extinguishment |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 |
Class C Preferred Units [Member] | Chief Financial Officer [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible shares, par value | $ / shares |  | $ 1.7749 |  |  | $ 1.7749 |  |  |  |  |  |  |  |  |  |
Redeemable convertible shares issued and sold | shares |  | 61,880 |  |  | 61,880 |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of preferred units, net of issuance costs |  | $ 100,000 |  |  | $ 100,000 |  |  |  |  |  |  |  |  |  |
Redeemable Convertible Preferred Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible shares, authorized | shares |  |  | 43,297,267 |  |  | 43,297,267 |  |  |  |  |  |  |  | 43,297,267 |
Redeemable convertible shares, par value | $ / shares |  |  | $ 0.001 |  |  | $ 0.001 |  |  |  |  |  |  |  | $ 0.001 |
Junior Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion price of redeemable preferred share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 6.0774 |  |
Original issue price, per share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 1.00 |  |
Preferred stock dividend rate |  |  |  |  |  |  |  |  |  |  |  |  | 5.00% |  |
Class A Preferred Unit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment of offering costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 170,000
Conversion price of redeemable preferred share | $ / shares |  | $ 15.5654 | 15.5715 |  | $ 15.5654 | 15.5715 |  |  |  |  |  |  | $ 23.7019 |  |
Fair value of tranche right |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,100,000
Original issue price, per share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | 3.90 |  |
Class B Preferred Unit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion price of redeemable preferred share | $ / shares |  | $ 16.7177 | $ 16.7256 |  | $ 16.7177 | $ 16.7256 |  |  |  |  |  |  | 26.7406 |  |
Original issue price, per share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | 4.40 |  |
Class C Preferred Units [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion price of redeemable preferred share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | 10.7868 |  |
Original issue price, per share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 1.7749 |  |

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- Definition Per share amount of par value or stated value of stock classified as temporary equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (27) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 480 -SubTopic 10 -Section S99 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=65877616&loc=d3e177068-122764 + Details
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