Stock-Based Compensation - Employee Stock Purchase Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from stock issued in connection with the employee stock purchase plan	$ 8,579	$ 0
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares reserved for issuance	1.50%
Common stock, annual increase (in shares)	8,000,000
Common stock reserved for issuance (in shares)	4,958,092
Percentage of employee earnings allowed	15.00%
Discount price percentage	85.00%
Offering period (up to)	27 months
Common stock purchased (in shares)	438,804
Share price (in USD per share)	$ 19.55
Employee contributions	$ 5,200
Unrecognized stock-based compensation expense	$ 6,700
Remaining offering period	1 year 3 months 18 days

Common Stock, Capital Shares Reserved For Future Issuance, Annual Increase

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Common Stock, Capital Shares Reserved For Future Issuance, Annual Increase, Percentage

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Share-based Compensation Arrangement By Share-based Payment Award, Discount Of Fair Market Value, Offering Date Or Purchase Date

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Share-based Compensation Arrangement by Share-based Payment Award, Offering Period

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Aggregate number of common shares reserved for future issuance.

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Total of the carrying values as of the balance sheet date of obligations incurred through that date and payable for obligations related to services received from employees, such as accrued salaries and bonuses, payroll taxes and fringe benefits.

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

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

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

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