Capitalization - Additional Information (Detail)						6 Months Ended
	Nov. 01, 2017 USD ($) $ / shares shares	Sep. 22, 2017 USD ($) $ / shares shares	Sep. 05, 2017	Aug. 25, 2017 USD ($) $ / shares shares	Aug. 08, 2017 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Dec. 31, 2017 $ / shares shares	Sep. 19, 2017 $ / shares shares	Mar. 31, 2017
Schedule of Capitalization, Equity [Line Items]
Stock conversion rate									100.00%
Stock split, conversion ratio			0.22222222
Forward stock split						1-to-4.5
Common stock, par value | $ / shares						$ 0.00001	$ 0.00001	$ 0.00001
Convertible preferred stock, par value | $ / shares						$ 0.00001	$ 0.00001	$ 0.00001
Common stock, shares authorized | shares						80,000,000	80,000,000	80,000,000
Convertible preferred stock, shares authorized | shares						20,000,000	20,000,000	20,000,000
Proceeds from issue of common stock | $						$ 10,000
Common stock, shares outstanding | shares						10,353,916	10,307,247
Preferred stock, shares outstanding | shares						0	0
Common stock, voting rights						The holders of shares of common stock are entitled to one vote for each share of common stock held
Common stock dividend, declared or paid | $						$ 0
Series A Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Shares issued, price per share | $ / shares					$ 7.66
Stock Purchase Agreement [Member]
Schedule of Capitalization, Equity [Line Items]
Common stock, par value | $ / shares	$ 0.00001
Number of additional shares issued and sold | shares	70,000
Shares issued, price per share | $ / shares	$ 11.00
Proceeds from issue of common stock | $	$ 770,000,000
Transaction closing date	Nov. 02, 2017
Director [Member]
Schedule of Capitalization, Equity [Line Items]
Number of additional shares issued and sold | shares				130,590
Shares issued, price per share | $ / shares				$ 7.66
Proceeds from issue of common stock | $				$ 1,000,000
IPO [Member]
Schedule of Capitalization, Equity [Line Items]
Number of additional shares issued and sold | shares		4,554,000
Shares issued, price per share | $ / shares		$ 10.00
Underwriting discounts and commissions | $		$ 3,200,000
Proceeds from initial offering of shares | $		42,300,000
Offering expenses | $		1,600,000
Net proceeds from issuance of common stock, after deducting offering expenses | $		$ 40,700,000
Conversion of preferred stock to common stock, shares | shares		2,061,773
Preferred stock conversion basis						1-to-1
Over-Allotment Option [Member]
Schedule of Capitalization, Equity [Line Items]
Number of additional shares issued and sold | shares		594,000
Sun Pharma Offering [Member] | Series A Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Shares issued, price per share | $ / shares					$ 7.66
Preferred stock, shares issued | shares					914,107
Aggregate proceeds from issuance of preferred stock | $					$ 7,000,000
Preferred stock, convertible beneficial conversion feature | $					$ 3,200,000