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Equity Incentive Plans and Stock-Based Compensation (Details 2) - $ / shares |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Apr. 23, 2015 | Apr. 24, 2014 | Apr. 30, 2012 | Apr. 30, 2009 | Jun. 30, 2012 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Stock Compensation Plan [Member] |  |  |  |  |  |  |  |  |  |  |
Stock-Based Compensation |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized |  |  | 10,000,000 |  | 6,500,000 | 6,500,000 |  |  |  |  | 4,000,000
Shares available for grant |  |  |  |  |  |  |  |  |  |  |
Shares available, at the beginning of the year |  |  |  |  |  |  | 7,305,368 |  | 11,173,545 |  | 10,724,228
Stock options granted (in shares) |  |  |  |  |  |  | (558,426) |  | (500,000) |  | (362,335)
Stock options forfeited (in shares) |  |  |  |  |  |  | 1,978,042 |  | 1,081,107 |  | 1,624,823
Stock options expired under former plans (in shares) |  |  |  |  |  |  |  |  | (412,467) |  | (657,878)
Nonvested equity stock and stock units granted (in shares) | [2] |  |  |  |  |  | (5,007,947) | [1] | (5,316,675) | [3] | (4,537,797)
Nonvested equity stock and stock units forfeited (in shares) | [2] |  |  |  |  |  | 1,334,110 |  | 1,279,858 |  | 382,504
Shares available, at the end of the period |  |  |  |  |  |  | 5,051,147 |  | 7,305,368 |  | 11,173,545
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 |  | 1.5 |  | 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 |  | 1.5 |  | 1.5
Potential Additional Performance Stock Units [Domain] |  |  |  |  |  |  |  |  |  |  |
Shares available for grant |  |  |  |  |  |  |  |  |  |  |
Nonvested equity stock and stock units granted (in shares) |  |  |  |  |  |  | 394,853 |  | 300,003 |  | 238,980
Options |  |  |  |  |  |  |  |  |  |  |
Shares available for grant |  |  |  |  |  |  |  |  |  |  |
Stock options granted (in shares) |  |  |  |  |  |  | (558,426) |  | (500,000) |  | (362,335)
Stock options forfeited (in shares) |  |  |  |  |  |  | 1,978,042 |  | 1,081,107 |  | 1,624,823
Options granted (in dollars per share) |  |  |  |  |  |  | $ 12.95 |  | $ 12.29 |  | $ 11.27
Expected weighted-average period for recognition of compensation cost (in years) |  |  |  |  |  |  | 2 years 5 months 16 days |  |  |  |
Employee Stock [Member] |  |  |  |  |  |  |  |  |  |  |
Stock-Based Compensation |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized |  | 2,000,000 | 1,500,000 | 1,500,000 |  |  |  |  |  |  |
Shares available for grant |  |  |  |  |  |  |  |  |  |  |
Shares available, at the end of the period |  |  |  |  |  |  | 836,273 |  |  |  |
Expected weighted-average period for recognition of compensation cost (in years) |  |  |  |  |  |  | 4 months |  |  |  |
[1] | Amount includes 300,003 shares that had been reserved for potential future issuance related to certain performance unit awards 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 Plan against the maximum number of shares authorized, each restricted stock granted reduces the number of shares available for grant by 1.5 shares and each restricted stock forfeited increases shares available for grant by 1.5 shares.
[3] | Amount includes 238,980 shares that had been reserved for potential future issuance related to certain performance unit awards discussed under the section titled "Nonvested Equity Stock and Stock Units" below.

X
- 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 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 decrease, for every restricted stock award granted. + References No definition available. + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Number of additional shares authorized for issuance under an established share-based compensation plan. + References No definition available. + 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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements. + References 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)(1)(iv)(4) -URI http://asc.fasb.org/extlink&oid=96867065&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://www.xbrl.org/2003/role/presentationRef -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=96867065&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://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 + Details
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