Stock Incentive Plans - RSUs and Stock Awards Granted (Details) - $ / shares	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
RSUs - Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants during period (shares)	1,547,049	1,891,335	1,751,823
Weighted-average grant date fair value (in dollars per share)	$ 13.35	$ 11.20	$ 13.28
Stock Awards - Board of Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants during period (shares)	65,520	59,880	54,120
Weighted-average grant date fair value (in dollars per share)	$ 13.43	$ 13.36	$ 14.78

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.

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