Stockholders' Equity - Employee Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 12,145	$ 4,079	$ 2,809
Unrecognized stock-based compensation cost	$ 18,200		$ 18,200
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)			6 years 7 days	6 years 7 days	5 years 11 months 15 days
Risk-free interest rate, minimum			1.55%	2.62%	1.90%
Risk-free interest rate, maximum			2.50%	3.00%	2.10%
Expected volatility, minimum			39.10%	40.20%	41.00%
Expected volatility, maximum			42.70%	41.50%	45.00%
Dividend yield			0.00%	0.00%	0.00%
Stock-based compensation expense	$ 7,900	$ 4,100			$ 2,800
Vested shares	0	0	0	0	0
Weighted-average period of recognition			2 years 9 months 18 days
Stock options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock (in shares)	$ 8.24	$ 1.93	$ 8.24	$ 1.93	$ 2.98
Stock options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock (in shares)	$ 22.70	$ 4.08	$ 22.70	$ 4.08	$ 3.58

Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Outstanding, Number

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

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Amount of cost to be recognized for option under share-based payment arrangement.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

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- Definition

The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The estimated measure of the minimum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

No definition available.

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The minimum risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

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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- Definition

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

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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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