Stock Plans Stock Plans (Schedule of Restricted Stock Units Grants by Type) (Details) - Restricted stock awards - $ / shares shares in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	1,544	1,796
Average grant date fair value (in dollars per share)	$ 6.12	$ 5.89
Service-based
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	1,111	1,270
Average grant date fair value (in dollars per share)	$ 5.70	$ 5.53
Performance objectives
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	78	158
Average grant date fair value (in dollars per share)	$ 5.85	$ 5.73
Market-condition
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	355	368
Average grant date fair value (in dollars per share)	$ 7.49	$ 7.22

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://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 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

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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