Share based compensation arrangement by share based payment award fair value amount of outstanding stock maximum.

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Share based compensation arrangement by share based payment award offering period.

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Share based compensation arrangement by share based payment award shares issued in period fair value.

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Share-based compensation arrangement by share-based payment award termination of employment.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Aggregate number of common shares reserved for future issuance.

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Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Amount of cash inflow from issuance of shares under share-based compensation arrangement, excluding stock option exercises.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Discount rate from fair value on offering date that participants pay for shares.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Number of share instruments newly issued under a share-based compensation plan.

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Intrinsic value of equity-based compensation awards not vested. Excludes stock and unit options.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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Stock Incentive Plans - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 21, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of options exercised (less than $0.2 million)		$ 15,100,000	$ 6,800,000	$ 200,000
Total unrecognized compensation costs related to stock options and RSUs		$ 17,700,000
Stock options and RSUs expected weighted average period		3 years 18 days
Weighted average fair value of options to purchase common stock granted (in dollars per share)		$ 17.74	$ 9.05	$ 1.60
Total fair value of options vested during period		$ 4,000,000.0
Shares available for issuance (in shares)		504,775	322,178
Stock-based compensation expense		$ 22,417,000	$ 7,138,000	$ 1,744,000
Share-based compensation expense, tax benefit recognized		0
Share-based compensation costs, capitalized		0
General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 11,804,000	3,700,000	994,000
Non Employee Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)		253,967
Fair value of shares issued		$ 1,300,000
Non Employee Director \| General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 200,000	$ 300,000	$ 200,000
2014 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance of common stock (in shares)		394,063
2016 Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance of common stock (in shares)		50,511
Maximum number of common stock shares that might be granted (in shares)					155,500
2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of common stock shares that might be granted (in shares)		60,200
2014 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum portion of earning an employee may contribute to the ESPP Plan		15.00%
Maximum value of shares which an employee can purchase per calendar year		$ 25,000
Offering period for employee stock purchases		6 months
Applicable exercise date an offering period shall be equal to percentage of the lower of fair market value of common stock		85.00%
Shares issued under ESPP (in shares)	20,528	51,712	76,710
Aggregate proceeds from the issuance of shares	$ 400,000	$ 800,000	$ 300,000
Shares available for issuance (in shares)		488,932
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value of RSUs vested during the period		$ 7,900,000
Intrinsic value of RSUs		32,700,000
Total unrecognized compensation costs related to stock options and RSUs		$ 22,900,000
Stock options and RSUs expected weighted average period		3 years 29 days
Restricted stock units \| 2016 Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Restricted stock units \| 2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period		10 years
Termination of employment		3 months
Vesting period		4 years
Stock Options \| 2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years