Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Dec. 08, 2020	Jul. 19, 2019	May 03, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stockholders Equity Note Disclosure [Line Items]
Common stock, shares issued	1,725,000	1,587,000	3,144,531	55,321,457	54,760,837
Common stock issue price per share	$ 181.00	$ 87.00	$ 64.00
Exercised number of shares				98,428
Net proceeds from public offering	$ 297,800	$ 131,100	$ 189,600		$ 297,775	$ 320,713
Stock-based compensation expense				$ 27,500	$ 17,007	12,847
Stock options, outstanding				625,107	696,711
Restricted stock units, outstanding				606,685	665,540
Aggregate intrinsic value of stock options exercised				$ 20,300	$ 36,600	$ 5,500
Weighted average grant date fair value of share-based awards granted				$ 88.01	$ 53.06	$ 31.27
Total fair value of stock options vested				$ 3,000	$ 2,800	$ 3,100
Total unrecognized compensation cost				$ 59,200
Unrecognized compensation cost, weighted average remaining requisite service period				3 years 1 month 28 days
Number of unvested options and restricted stock units				1,953,733
Incentive options, term				10 years
2018 Plan
Stockholders Equity Note Disclosure [Line Items]
Common stock shares reserved for Issuance							2,778,000
Incentive options, vesting period				2,127,217
Employee Stock Option | Minimum
Stockholders Equity Note Disclosure [Line Items]
Incentive options, vesting period				3 years
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
Employee Stock Option | Maximum | Vest Over Five Year
Stockholders Equity Note Disclosure [Line Items]
Incentive options, vesting percentage				33.00%
Option To Purchase Common Stock
Stockholders Equity Note Disclosure [Line Items]
Stock options, outstanding				625,107	696,711	957,559
Restricted Stock Units (RSUs)
Stockholders Equity Note Disclosure [Line Items]
Restricted stock units, outstanding				606,685	665,540	734,984
Closing price of common stock				$ 264.84
Unvested Options [Member]
Stockholders Equity Note Disclosure [Line Items]
Incentive options, vesting period				5 years
Restricted Stock And Performance Stock Units [Member]
Stockholders Equity Note Disclosure [Line Items]
Restricted stock units, outstanding				606,685
Closing price of common stock				$ 264.84
Aggregate intrinsic value of restricted stock units vested				$ 46,500	$ 28,300	$ 17,500
Weighted average grant date fair value of restricted stock units granted				$ 222.17	$ 109.69	$ 67.22
Total grant date fair value of restricted stock units vested				$ 13,900	$ 10,800	$ 8,500
Non Employee Director Stock Option[Member]
Stockholders Equity Note Disclosure [Line Items]
Estimated forfeiture rates				0.00%
Incentive options, vesting period				9 years
Underwriters | Common Stock
Stockholders Equity Note Disclosure [Line Items]
Exercised number of shares	225,000	207,000	410,156
Non-Executive [Member] | Employee Stock Option
Stockholders Equity Note Disclosure [Line Items]
Estimated forfeiture rates				8.00%
Non-Executive [Member] | Restricted Stock And Performance Stock Units [Member]
Stockholders Equity Note Disclosure [Line Items]
Estimated forfeiture rates				8.00%
Executive Officer [Member] | Employee Stock Option
Stockholders Equity Note Disclosure [Line Items]
Estimated forfeiture rates				3.00%
Executive Officer [Member] | Restricted Stock And Performance Stock Units [Member]
Stockholders Equity Note Disclosure [Line Items]
Estimated forfeiture rates				3.00%