Redeemable Convertible Preferred Shares - Additional Information (Detail)				1 Months Ended					12 Months Ended
	Oct. 20, 2017	Jun. 30, 2017 $ / shares	Jul. 01, 2015 USD ($) $ / shares shares	Jul. 31, 2017 USD ($) $ / shares shares	Mar. 31, 2017 USD ($) $ / shares shares	Feb. 29, 2016 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Jan. 31, 2015 USD ($) $ / shares 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 into preferred units									$ 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
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 into 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 into preferred units			$ 8,000,000
Redeemable issuer option value			$ 900,000
Redeemable convertible shares, issued | 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 | 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 into 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
Conversion of bridge units into preferred units										8,500,000
Redeemable issuer option value										$ 900,000
Redeemable convertible shares, issued | shares					24,326,470					5,321,112
Proceeds from issuance of preferred units, net of issuance costs					$ 43,000,000
Payment of offering costs					$ 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
Redeemable convertible shares, issued | shares				61,880
Proceeds from issuance of preferred units, net of issuance costs				$ 100,000
Redeemable Convertible Preferred Shares [Member]
Class of Stock [Line Items]
Redeemable convertible shares, authorized | shares										43,297,267
Redeemable convertible shares, par value | $ / shares										$ 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		$ 15.5715		$ 15.5654					$ 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		$ 16.7256		$ 16.7177					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