Stock-based Awards (Details 2 - RSUs) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Weighted-Average Grant Date Fair Value
Stock based compensation expense	$ 8,635	$ 9,097
Non-vested restricted stock unit awards
Number of Shares
Non-vested at the beginning of period (in shares)	5,375,963
Granted (in shares)	3,361,668
Vested (in shares)	(505,104)
Canceled/forfeited (in shares)	(623,122)
Non-vested at the end of the period (in per share)	7,609,405
Weighted-Average Grant Date Fair Value
Non-vested at the beginning of period (in dollars per share)	$ 11.01
Granted (in dollars per share)	7.10
Vested (in dollars per share)	10.48
Canceled/forfeited (in dollars per share)	10.84
Non-vested at the end of the period (in dollars per share)	$ 9.33
Remaining stock based compensation expense for non vested restricted stock units	$ 68,200
Weighted average period over which remaining stock based compensation expense for unvested awards is expected to be recognized	2 years 9 months 7 days
Stock based compensation expense	$ 5,500	$ 4,400

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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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 number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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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The weighted average fair value at grant date for nonvested equity-based awards issued 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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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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