Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Jul. 19, 2019	May 03, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Stockholders Equity Note Disclosure [Line Items]
Common stock, shares issued	1,587,000	3,144,531	52,278,083		52,078,258
Common stock issue price per share	$ 87.00	$ 64.00
Exercised number of shares			67,877
Net proceeds from public offering	$ 131,100	$ 189,600
Stock-based compensation expense			$ 4,165	$ 3,251
Stock options, outstanding			915,518	1,027,831	957,559
Closing price of common stock			$ 96.54
Aggregate intrinsic value of stock options exercised			$ 4,700	$ 100
Weighted average grant date fair value of share-based awards granted			$ 41.77	$ 30.21
Total fair value of stock options vested			$ 2,000	$ 2,200
Total unrecognized compensation cost			$ 43,700
Unrecognized compensation cost, weighted average remaining requisite service period			3 years 10 months 24 days
Number of unvested options and restricted stock units			1,721,681
2018 Plan
Stockholders Equity Note Disclosure [Line Items]
Common stock shares reserved for Issuance						2,778,000
Incentive options, vesting period			2,419,406
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			716,630	680,549	734,984
Closing price of common stock			$ 96.54
Aggregate intrinsic value of restricted stock units vested			$ 11,800	$ 9,500
Weighted average grant date fair value of restricted stock units granted			$ 57.85	$ 31.79
Total grant date fair value of restricted stock units vested			$ 5,300	$ 4,900
Underwriters | Common Stock
Stockholders Equity Note Disclosure [Line Items]
Exercised number of shares	207,000	410,156