Stockholders' Equity and Equity Compensation - Summary of Deferred Stock Unit Activity (Details)	9 Months Ended
Sep. 30, 2018 $ / shares shares
Deferred Stock Units
Outstanding, beginning balance (in shares) \| shares	1,428,878
Outstanding, ending balance (in shares) \| shares	1,190,207
Weighted Average Award Date Fair Value
Outstanding, beginning balance (in dollars per share) \| $ / shares	$ 21.53
Outstanding, ending balance (in dollars per share) \| $ / shares	$ 23.26
Deferred Stock Units
Deferred Stock Units
Outstanding, beginning balance (in shares) \| shares	269,977
Awarded (in shares) \| shares	43,729
Distributed (in shares) \| shares	(26,396)
Outstanding, ending balance (in shares) \| shares	287,310
Weighted Average Award Date Fair Value
Outstanding, beginning balance (in dollars per share) \| $ / shares	$ 20.14
Awarded (in dollars per share) \| $ / shares	23.67
Distributed (in dollars per share) \| $ / shares	19.32
Outstanding, ending balance (in dollars per share) \| $ / shares	$ 20.76

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).

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 (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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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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- 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

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-Paragraph 2
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- Definition

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 weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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- Definition

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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