Stock-Based Compensation - Restricted Stock Activity (Details) - Restricted stock awards	6 Months Ended
Jun. 30, 2019 shares
Restricted Stock Awards
Outstanding, beginning of period (in shares)	2,356,418
Granted (in shares)	2,025,337
Vested (in shares)	(697,782)
Forfeited (in shares)	(82,952)
Outstanding, end of period (in shares)	3,601,021
Minimum
Additional information
Vesting period	3 years
Maximum
Additional information
Vesting period	4 years

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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-SubTopic 10
-Section 50
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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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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 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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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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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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