Redeemable Convertible Preferred Stock - Additional Information (Detail)		1 Months Ended			12 Months Ended
	Jul. 05, 2017 USD ($) $ / shares shares	Feb. 28, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Jan. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) Director Installment $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 shares
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			151,557,293		0	151,557,293
Redeemable convertible preferred stock, par value (in dollars per share) | $ / shares			$ 0.01		$ 0.01	$ 0.01
Preferred stock shares issued		483,501
Preferred stock shares issued, price per share | $ / shares		$ 1.36
Proceeds from issuance of redeemable convertible preferred stock | $		$ 626,000
Preferred stock issuance costs, paid | $		$ 32,000			$ 2,304,000	$ 180,000	$ 1,320,000
Number of common shares issued on conversion of redeemable convertible preferred stock			10,461,117			10,461,117
Redeemable convertible preferred stock, issued (in shares)			105,631,019		0	105,631,019
Redeemable convertible preferred stock, outstanding (in shares)			105,631,019		0	105,631,019	81,975,780	81,975,780
Preferred stock, voting rights description					The holders of the Redeemable Preferred Stock were entitled to vote, together with the holders of common stock, on all matters submitted to stockholders for a vote and had the right to vote the number of shares equal to the number of whole shares of common stock into which such holders of Redeemable Preferred Stock could convert on the record date for determination of stockholders entitled to vote. In addition, holders of the Senior Preferred Stock, voting as a single class, were entitled to elect three directors of the Company. The holders of the Junior Preferred Stock, voting as a single class, were entitled to elect two directors of the Company.
Dividends declared | $					$ 0	$ 0
Dividends paid | $					$ 0	$ 0
Percentage of voting to be held by holders of senior preferred stock for deemed liquidation event					55.00%
Redemption date of redeemable preferred stock					Dec. 22, 2020
Number of annual installments for redemption | Installment					3
IPO [Member]
Temporary Equity [Line Items]
Initial public offering completion date					Jul. 05, 2017
IPO [Member] | Common Stock [Member]
Temporary Equity [Line Items]
Preferred stock shares issued, price per share | $ / shares	$ 15.00
Preferred stock issuance costs, paid | $	$ 2,304,000
Number of common shares issued on conversion of redeemable convertible preferred stock	10,509,774
Underwritten public offering costs | $	$ 3,937,000
Series E-1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock shares issued				9,705,882		9,705,882
Preferred stock shares issued, price per share | $ / shares				$ 1.36
Proceeds from issuance of redeemable convertible preferred stock | $				$ 13,183,000
Preferred stock issuance costs, paid | $				$ 17,000
Preferred stock shares converted		4,411,765	16,567,108
Series F Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock shares issued		483,501	13,949,357		483,501	13,949,357
Preferred stock shares issued, price per share | $ / shares		$ 1.36	$ 1.36			$ 1.36
Proceeds from issuance of redeemable convertible preferred stock | $		$ 626,000	$ 18,806,000
Preferred stock issuance costs, paid | $		$ 32,000	$ 165,000
Stock purchase agreement, additional shares agreed to purchase		274,957	8,192,477
Stock purchase agreement, price per share | $ / shares		$ 1.36	$ 1.36
Stock purchase agreement, aggregate purchase price | $		$ 11,516,000	$ 11,142,000
Stock purchase agreement, shares authorized		758,458
Stock purchase agreement, aggregate number of shares agreed to purchase		8,467,434
Series E- Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock shares converted			8,927,582
Series E-2 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock shares issued on conversion			8,927,582
Series E-3 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock shares issued on conversion		4,411,765	16,567,108
Senior Preferred Stock [Member]
Temporary Equity [Line Items]
Number of directors entitled to be elected | Director					3
Junior Preferred Stock [Member]
Temporary Equity [Line Items]
Number of directors entitled to be elected | Director					2
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			1,250,000			1,250,000
Number of common shares issued on conversion of redeemable convertible preferred stock			12,579			12,579
Redeemable convertible preferred stock, issued (in shares)			1,250,000			1,250,000
Redeemable convertible preferred stock, outstanding (in shares)			1,250,000			1,250,000
Noncumulative dividends entitled to receive by redeemable preferred stock holders | $ / shares					$ 0.08
Original issue price per share | $ / shares					1.00
Liquidation preference per share | $ / shares					1.00
Conversion price of Redeemable Preferred | $ / shares					99.37
Series A-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			615,384			615,384
Number of common shares issued on conversion of redeemable convertible preferred stock			6,192			6,192
Redeemable convertible preferred stock, issued (in shares)			615,384			615,384
Redeemable convertible preferred stock, outstanding (in shares)			615,384			615,384
Noncumulative dividends entitled to receive by redeemable preferred stock holders | $ / shares					0.104
Original issue price per share | $ / shares					1.30
Liquidation preference per share | $ / shares					1.30
Conversion price of Redeemable Preferred | $ / shares					129.181
Series B Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			3,706,056			3,706,056
Number of common shares issued on conversion of redeemable convertible preferred stock			372,955			372,955
Redeemable convertible preferred stock, issued (in shares)			3,706,056			3,706,056
Redeemable convertible preferred stock, outstanding (in shares)			3,706,056			3,706,056
Noncumulative dividends entitled to receive by redeemable preferred stock holders | $ / shares					0.03251
Original issue price per share | $ / shares					0.4064
Liquidation preference per share | $ / shares					0.4064
Conversion price of Redeemable Preferred | $ / shares					4.038397
Series C-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			5,934,050			5,934,050
Number of common shares issued on conversion of redeemable convertible preferred stock			597,167			597,167
Redeemable convertible preferred stock, issued (in shares)			5,934,050			5,934,050
Redeemable convertible preferred stock, outstanding (in shares)			5,934,050			5,934,050
Noncumulative dividends entitled to receive by redeemable preferred stock holders | $ / shares					0.09437
Original issue price per share | $ / shares					1.179633
Liquidation preference per share | $ / shares					1.179633
Conversion price of Redeemable Preferred | $ / shares					11.722013
Series C-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			8,689,144			8,689,144
Number of common shares issued on conversion of redeemable convertible preferred stock			874,423			874,423
Redeemable convertible preferred stock, issued (in shares)			8,689,144			8,689,144
Redeemable convertible preferred stock, outstanding (in shares)			8,689,144			8,689,144
Noncumulative dividends entitled to receive by redeemable preferred stock holders | $ / shares					0.09437
Original issue price per share | $ / shares					1.179633
Liquidation preference per share | $ / shares					1.179633
Conversion price of Redeemable Preferred | $ / shares					11.722013
Series D Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			34,142,865			34,142,865
Number of common shares issued on conversion of redeemable convertible preferred stock			3,435,932			3,435,932
Redeemable convertible preferred stock, issued (in shares)			34,142,865			34,142,865
Redeemable convertible preferred stock, outstanding (in shares)			34,142,865			34,142,865
Noncumulative dividends entitled to receive by redeemable preferred stock holders | $ / shares					0.09437
Original issue price per share | $ / shares					1.179633
Liquidation preference per share | $ / shares					1.179633
Conversion price of Redeemable Preferred | $ / shares					11.722013
Series D-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			363,636			363,636
Number of common shares issued on conversion of redeemable convertible preferred stock			36,594			36,594
Redeemable convertible preferred stock, issued (in shares)			363,636			363,636
Redeemable convertible preferred stock, outstanding (in shares)			363,636			363,636
Noncumulative dividends entitled to receive by redeemable preferred stock holders | $ / shares					0.40
Original issue price per share | $ / shares					5.50
Liquidation preference per share | $ / shares					5.50
Series E-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			24,264,705			24,264,705
Number of common shares issued on conversion of redeemable convertible preferred stock			774,639			774,639
Redeemable convertible preferred stock, issued (in shares)			7,697,597			7,697,597
Redeemable convertible preferred stock, outstanding (in shares)			7,697,597			7,697,597
Noncumulative dividends entitled to receive by redeemable preferred stock holders | $ / shares					0.1088
Original issue price per share | $ / shares					1.36
Liquidation preference per share | $ / shares					1.36
Conversion price of Redeemable Preferred | $ / shares					13.51432
Series E Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			12,715,822			12,715,822
Number of common shares issued on conversion of redeemable convertible preferred stock			381,225			381,225
Redeemable convertible preferred stock, issued (in shares)			3,788,240			3,788,240
Redeemable convertible preferred stock, outstanding (in shares)			3,788,240			3,788,240
Original issue price per share | $ / shares					1.179633
Liquidation preference per share | $ / shares					1.179633
Conversion price of Redeemable Preferred | $ / shares					11.722013
Series E-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			9,226,082			9,226,082
Number of common shares issued on conversion of redeemable convertible preferred stock			898,418			898,418
Redeemable convertible preferred stock, issued (in shares)			8,927,582			8,927,582
Redeemable convertible preferred stock, outstanding (in shares)			8,927,582			8,927,582
Original issue price per share | $ / shares					1.179633
Liquidation preference per share | $ / shares					1.179633
Conversion price of Redeemable Preferred | $ / shares					11.722013
Series E-3 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			21,237,785			21,237,785
Number of common shares issued on conversion of redeemable convertible preferred stock			1,667,214			1,667,214
Redeemable convertible preferred stock, issued (in shares)			16,567,108			16,567,108
Redeemable convertible preferred stock, outstanding (in shares)			16,567,108			16,567,108
Original issue price per share | $ / shares					1.36
Liquidation preference per share | $ / shares					1.36
Conversion price of Redeemable Preferred | $ / shares					13.51432
Series F Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares)			29,411,764			29,411,764
Number of common shares issued on conversion of redeemable convertible preferred stock			1,403,779			1,403,779
Redeemable convertible preferred stock, issued (in shares)			13,949,357			13,949,357
Redeemable convertible preferred stock, outstanding (in shares)			13,949,357			13,949,357
Original issue price per share | $ / shares					1.36
Liquidation preference per share | $ / shares					1.36
Conversion price of Redeemable Preferred | $ / shares					$ 13.51432
Redeemable Convertible Preferred Stock [Member] | Maximum [Member]
Temporary Equity [Line Items]
Underwritten public offering costs | $					$ 150,000,000
Redeemable Convertible Preferred Stock [Member] | Minimum [Member]
Temporary Equity [Line Items]
Gross proceeds from issuance of redeemable convertible preferred stock | $					$ 50,000,000
Redeemable Convertible Preferred Stock [Member] | IPO [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, outstanding (in shares)	106,114,520