Stock-based Compensation - Compensation Expense by Award (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock-Based Compensation
Grant date fair value	$ 100	$ 58	$ 26,741	$ 25,643
Stock-based compensation expense	$ 8,532	$ 4,243	$ 20,766	$ 14,633
Stock Options
Stock-Based Compensation
Granted (in units)			674	861
Grant date fair value			$ 6,147	$ 5,772
Exercised (in units)	55	9	285	34
Performance-based RSUs
Stock-Based Compensation
Granted (in units)			524	694
Grant date fair value			$ 12,791	$ 12,512
Vested (in units)			774	446
Time-based RSUs
Stock-Based Compensation
Granted (in units)	5	3	321	408
Grant date fair value	$ 100	$ 58	$ 7,803	$ 7,359
Vested (in units)	1	4	245	165

Fair value of share-based payments awards options and other than options granted.

No definition available.

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- Definition

Fair value of share-based payments awards options granted.

+ References

No definition available.

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- Definition

Fair value of share-based payments awards other than options granted.

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No definition available.

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- Definition

Number of options exercised.

+ References

No definition available.

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

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).

+ References

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

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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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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- Definition

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

+ References

No definition available.

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