Share Based Awards - Options activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Options Activity Rollforward
Number of Shares Available for Issuance, Beginning Balance		2,337,545
Options Outstanding, Number, Beginning Balance		4,496,557
Number of Shares Available for Issuance, Authorized		5,310,327
Number of Shares Available for Issuance, Granted	0	(125,000)
Options Outstanding, Shares Granted		125,000
Number of Shares Available for Issuance, other than Options granted		(2,170,855)
Options exercised		(1,337,433)
Number of Shares Available for Issuance, Cancelled		355,029
Number of Shares Available for Issuance, Ending Balance	1,365,303	1,365,303	2,337,545
Options Outstanding, Number, Ending Balance	2,929,095	2,929,095	4,496,557
Vested and exercisable- end of the period	2,374,402	2,374,402
Vested and expected to vest - end of the period	2,837,136	2,837,136
Options Activity, Weighted Average Exercise Price Rollforward
Options Outstanding, Weighted-Average Exercise Price, Beginning Balance		$ 5.02
Options Outstanding, Weighted Average Exercise Price Granted		4.52
Options Outstanding, Weighted Average Exercise Price Exercised		4.10
Options Outstanding, Weighted Average Exercise Price Cancelled		6.99
Options Outstanding, Weighted-Average Exercise Price, Ending Balance	$ 5.18	5.18	$ 5.02
Options Outstanding, Weighted-Average Exercise Price, Vested and exercisable	5.36	5.36
Options Outstanding, Weighted-Average Exercise Price, Vested and expected to vest	$ 5.21	$ 5.21
Options Outstanding, Weighted-Average Remaining Contractual Term (Years)		5 years 3 months 7 days	4 years 11 months 23 days
Options Outstanding, Weighted-Average Remaining Contractual Term Vested and exercisable (Years)		4 years 5 months 23 days
Options Outstanding, Weighted-Average Remaining Contractual Term Vested and expected to vest (Years)		5 years 1 month 28 days
Options Outstanding, Aggregate Intrinsic Value	$ 4,877	$ 4,877	$ 2,446
Options Outstanding, Vested and exercisable, Aggregate Intrinsic Value	3,703	3,703
Options Outstanding, Vested and expected to vest, Aggregate Intrinsic Value	$ 4,688	$ 4,688
RSUs, excluding Bonus Plans
Options Activity Rollforward
Number of Shares Available for Issuance, other than Options granted		(7,568,016)
Restricted stock units
Options Activity Rollforward
Number of Shares Available for Issuance, other than Options granted		(9,738,871)
Shares withheld for net settlement of equity awards (in shares)		1,064,577
Number of Shares Available for Issuance, Restricted stock units cancelled		2,161,696

Number of shares that have been withheld for net settlement of equity awards during the period.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Net number of non-option equity instruments granted to participants.

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Number of additional shares authorized for issuance under share-based payment arrangement.

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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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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest exercisable options that may be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest exercisable or convertible options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of share options (or share units) exercised during the current period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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