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Share-Based Payments - Summary of Performance and Phantom Shares by Grant Year (Details)	12 Months Ended
	Dec. 31, 2017 shares
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding (in shares)	208,922
Phantom Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding (in shares)	118,680
Grants 2015 | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	277,585
Vested (in shares)	107,882
Forfeited (in shares)	169,703
Outstanding (in shares)	0
Grants 2015 | Phantom Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	135,651
Vested (in shares)	52,719.8395718475
Forfeited (in shares)	82,931.1604281525
Outstanding (in shares)	0
Grants 2016 | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	278,477
Vested (in shares)	28,566
Forfeited (in shares)	168,224
Outstanding (in shares)	81,687
Grants 2016 | Phantom Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	147,513
Vested (in shares)	15,131.9787096774
Forfeited (in shares)	96,977.9012903226
Outstanding (in shares)	35,403
Grants 2017 | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	216,878
Vested (in shares)	0
Forfeited (in shares)	89,643
Outstanding (in shares)	127,235
Grants 2017 | Phantom Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	173,619
Vested (in shares)	0
Forfeited (in shares)	90,341.775812609
Outstanding (in shares)	83,277

X

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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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.

+ References

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