Stock-Based Compensation (Narrative) (Details)	12 Months Ended
Dec. 31, 2017 USD ($) shares
The 2009 ESPP
Number of shares authorized (in shares)	1,500,000
Maximum employee subscription rate (in percent)	10.00%
Maximum amount of stock per employee \| $	$ 25,000
Purchase price of common stock (in percent)	85.00%
Discount from market price, offering date (in percent)	15.00%
Shares available for purchase (in shares)	281,870
2013 Stock Incentive Plan
Number of shares authorized (in shares)	3,800,000.0
Shares available for purchase (in shares)	1,383,827
2013 Stock Incentive Plan \| Time Vesting RSU
Issuance of restricted stock to employees (in shares)	52,056
2013 Stock Incentive Plan \| Performance and Time Vesting RSU's
Issuance of restricted stock to employees (in shares)	110,300
2013 Stock Incentive Plan \| Performance RSU
Issuance of restricted stock to employees (in shares)	83,510
2013 Stock Incentive Plan \| Restricted Stock Units (RSUs)
Award vesting period	4 years
Weighted average attainment level for performance and time vesting RSUs (in percent)	57.20%
Unvested RSUs \| $	$ 12,500,000
Weighted average vesting period	2 years 1 month 6 days
2013 Stock Incentive Plan \| Restricted Stock Units (RSUs) \| Maximum
Award vesting period	4 years

The maximum amount of stock per employee under share based compensation arrangement.

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- Definition

Represents the weighted average attainment level associated with performance and time-vesting RSUs.

+ References

No definition available.

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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.

+ 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 (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

+ References

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ 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 (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Discount rate from fair value on offering date that participants pay for shares.

+ References

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

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- Definition

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

+ References

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ 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 (a)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

+ References

No definition available.

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- Definition

Total number of shares issued during the period, including shares forfeited, as a result of Restricted Stock Awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

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-Publisher FASB
-Name Accounting Standards Codification
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