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Equity Incentive Plans and Stock-Based Compensation (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018
Employee Stock [Member] |  |  |
Stock-Based Compensation |  |  |
Stock-based compensation |  | $ 0.5 | $ 0.5
Shares available for grant |  |  |
Shares available, at the end of the period |  | 2,294,878 |
Stock-Based Incentive Compensation Plans |  |  |
Shares available for grant |  |  |
Shares available, at the beginning of the year |  | 10,074,046 |
Stock options granted (in shares) |  | 0 |
Stock options forfeited (in shares) |  | 33,967 |
Nonvested equity stock and stock units granted (in shares) | [1],[2] | (5,907,629) |
Nonvested equity stock and stock units forfeited (in shares) | [2] | 315,349 |
Shares available, at the end of the period |  | 4,515,733 |
Conversion factor used to calculate the decrease in the number of shares available for grant resulting from the grant of restricted stock awards |  | 1.5 |
Conversion factor used to calculate the increase in the number of shares available for grant resulting from the forfeiture of restricted stock awards |  | 1.5 |
Restricted Stock and Stock Units [Member] |  |  |
Stock-Based Compensation |  |  |
Stock-based compensation |  | $ 6.4 | $ 6.5
Potential Additional Performance Stock Units [Domain] |  |  |
Shares available for grant |  |  |
Nonvested equity stock and stock units granted (in shares) | [1],[2] | 853,313 |
[1] | Amount includes approximately 0.9 million shares that have been reserved for potential future issuance related to certain performance unit awards granted in the first quarter of 2019 and discussed under the section titled "Nonvested Equity Stock and Stock Units" below.
[2] | For purposes of determining the number of shares available for grant under the 2015 Equity Incentive Plan (the “2015 Plan”) against the maximum number of shares authorized, each share of restricted stock granted reduces the number of shares available for grant by 1.5 shares and each share of restricted stock forfeited increases shares available for grant by 1.5 shares.

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- Definition Represents the increase in number of shares available for grant under the stock incentive plans, which is based on a factor of 1.5 for every restricted stock award forfeited for the period. + References No definition available. + Details
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- Definition For purposes of determining the number of shares available for grant under the 2006 Equity Incentive Plan, represents the multiplier by which the number of shares available for grant will increase, for every restricted stock award forfeited. + References No definition available. + Details
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- Definition Represents the decrease in number of shares available for grant under the stock incentive plans, which is based on a factor of 1.5 for every restricted stock award granted for the period. + References No definition available. + Details
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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Net number of share options (or share units) granted during the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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