Stock Plans Stock Plans (Schedule of Restricted Stock Units Grants by Type) (Details) - Restricted stock unit awards - $ / shares shares in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)	$ 5.54	$ 5.88	$ 6.14	$ 5.96
Restricted stock units, granted (in shares)	200	444	1,534	1,414
Service-based
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)	$ 5.43	$ 5.73	$ 5.72	$ 5.52
Restricted stock units, granted (in shares)	180	255	1,101	922
Performance objectives
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)		$ 5.73	$ 5.85	$ 5.73
Restricted stock units, granted (in shares)	0	158	78	158
Market condition restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)	$ 6.56	$ 7.89	$ 7.49	$ 7.27
Restricted stock units, granted (in shares)	20	31	355	334

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

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