Employee Benefit Plans - Unamortized Stock-based Compensation (Details) $ in Thousands	6 Months Ended
Jun. 30, 2019 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation (in thousands)	$ 126,684
Weighted average vesting period (in years)	1 year 3 months 18 days
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation (in thousands)	$ 42,318
Weighted average vesting period (in years)	2 years 2 months 12 days
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation (in thousands)	$ 5,036
Weighted average vesting period (in years)	2 years 9 months 18 days
Restricted Stock Units (Service-Based)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation (in thousands)	$ 61,393
Weighted average vesting period (in years)	2 years 10 months 24 days
Restricted Stock Units (Performance-Based)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation (in thousands)	$ 13,633
Weighted average vesting period (in years)	1 year 3 months 18 days
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation (in thousands)	$ 4,304
Weighted average vesting period (in years)	1 year 6 months

Unrecognized cost of unvested share-based compensation awards.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

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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- 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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