Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
	May 03, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Stockholders Equity Note Disclosure [Line Items]
Common stock, shares issued	3,144,531	48,086,422		48,086,422		43,917,378
Common stock issue price per share	$ 64.00
Exercised number of shares				57,956
Net proceeds from public offering	$ 189,600			$ 189,623
Stock-based compensation expense		$ 3,031	$ 2,625	$ 6,283	$ 4,893
Incentive options, vesting period				3 years
Stock options, outstanding		985,266		985,266		998,226
Closing price of common stock		$ 85.95		$ 85.95
Aggregate intrinsic value of stock options exercised				$ 3,600	$ 2,400
Weighted average grant date fair value of share-based awards granted				$ 30.07	$ 18.41
Total fair value of stock options vested				$ 2,700	$ 1,800
Total unrecognized compensation cost		$ 38,700		$ 38,700
Unrecognized compensation cost, weighted average remaining requisite service period				4 years 1 month 24 days
Number of unvested options and restricted stock units		1,672,980		1,672,980
2018 Plan
Stockholders Equity Note Disclosure [Line Items]
Common stock shares reserved for Issuance						2,778,000
Incentive options, vesting period		2,596,600		2,596,600
Employee Stock Option | Minimum | Vest Over Three Year
Stockholders Equity Note Disclosure [Line Items]
Incentive options, vesting percentage				20.00%
Employee Stock Option | Maximum
Stockholders Equity Note Disclosure [Line Items]
Incentive options, vesting period				5 years
Incentive options, term				10 years
Employee Stock Option | Maximum | Vest Over Five Year
Stockholders Equity Note Disclosure [Line Items]
Incentive options, vesting percentage				33.00%
Non-Employee Directors
Stockholders Equity Note Disclosure [Line Items]
Incentive options, vesting period				1 year
Option To Purchase Common Stock
Stockholders Equity Note Disclosure [Line Items]
Stock options, outstanding		985,266	1,058,834	985,266	1,058,834
Restricted Stock Units (RSUs)
Stockholders Equity Note Disclosure [Line Items]
Restricted stock units, outstanding		766,986	716,996	766,986	716,996	707,413
Closing price of common stock		$ 85.95		$ 85.95
Aggregate intrinsic value of restricted stock units vested				$ 11,700	$ 4,200
Weighted average grant date fair value of restricted stock units granted				$ 31.97	$ 34.47
Total grant date fair value of restricted stock units vested				$ 6,000	$ 3,300
Unvested Options
Stockholders Equity Note Disclosure [Line Items]
Incentive options, vesting period				5 years
Underwriters | Common Stock
Stockholders Equity Note Disclosure [Line Items]
Exercised number of shares	410,156