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The cash inflow from the additional capital contribution to the entity.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Price of a single share of a number of saleable stocks of a company.

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Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		6 Months Ended
	Jul. 19, 2019	May 03, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Stockholders Equity Note Disclosure [Line Items]
Common stock, shares issued	1,587,000	3,144,531	52,494,884		52,494,884		52,078,258
Common stock issue price per share	$ 87.00	$ 64.00
Exercised number of shares					246,353
Net proceeds from public offering	$ 131,100	$ 189,600				$ 189,623
Stock-based compensation expense			$ 4,102	$ 3,031	$ 8,267	$ 6,283
Stock options, outstanding			768,904	985,266	768,904	985,266	957,559
Closing price of common stock			$ 123.61		$ 123.61
Aggregate intrinsic value of stock options exercised					$ 2,500	$ 3,600
Weighted average grant date fair value of share-based awards granted					$ 46.56	$ 30.07
Total fair value of stock options vested					$ 2,500	$ 2,700
Total unrecognized compensation cost			$ 42,800		$ 42,800
Unrecognized compensation cost, weighted average remaining requisite service period					3 years 9 months 29 days
Number of unvested options and restricted stock units			1,761,586		1,761,586
2018 Plan
Stockholders Equity Note Disclosure [Line Items]
Common stock shares reserved for Issuance								2,778,000
Incentive options, vesting period			2,370,882		2,370,882
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%
Non-Employee Directors
Stockholders Equity Note Disclosure [Line Items]
Incentive options, vesting period					1 year
Option To Purchase Common Stock \| Minimum
Stockholders Equity Note Disclosure [Line Items]
Incentive options, term					10 years
Unvested Options
Stockholders Equity Note Disclosure [Line Items]
Incentive options, vesting period					5 years
Restricted Stock Units and Performance Stock Units
Stockholders Equity Note Disclosure [Line Items]
Restricted stock units, outstanding			696,098	766,986	696,098	766,986	734,984
Closing price of common stock			$ 123.61		$ 123.61
Aggregate intrinsic value of restricted stock units vested					$ 16,600	$ 11,700
Weighted average grant date fair value of restricted stock units granted					$ 59.84	$ 31.97
Total grant date fair value of restricted stock units vested					$ 7,300	$ 6,000
Underwriters \| Common Stock
Stockholders Equity Note Disclosure [Line Items]
Exercised number of shares	207,000	410,156