Stock-Based Compensation Restricted Stock Units Summary (Details) - Restricted Stock Units (RSUs) [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
[Line Items]
Outstanding, beginning balance, Number	701	756	682
Outstanding, Weighted Average Grant Date Fair Value	$ 47.68	$ 38.04
Granted, Number	273	306	434
Granted, Weighted-average grant date fair value	$ 50.95	$ 41.58	$ 35.09
Forfeited, Number	(46)	(49)	(64)
Forfeitures, Weighted Average Grant Date Fair Value	$ 48.56
Outstanding, ending balance, Number	556	701	756
Vested and Released [Member]
[Line Items]
Issued, Number	(372)	(312)	(296)
Released, Weighted Average Grant Date Fair Value	$ 36.93
Released, Aggregate Intrinsic Value	$ 14,219	$ 11,944	$ 12,204
Vested but Not Released [Member]
[Line Items]
Issued, Number	(142)
Released, Aggregate Intrinsic Value	$ 9,650
Expected to Vest [Member]
[Line Items]
Outstanding, ending balance, Number	350
Expected to vest, Aggregate Intrinsic Value	$ 23,877

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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

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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).

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-Publisher FASB
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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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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.

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-Publisher FASB
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-SubTopic 10
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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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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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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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Intrinsic value of equity-based compensation awards not vested. Excludes stock and unit options.

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Intrinsic value of equity-based compensation awards vested. Excludes stock and unit options.

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Number of shares related to Restricted Stock Award forfeited during the period.

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Number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of any shares forfeited. Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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