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Equity Incentive Plans and Stock-Based Compensation (Details 2) - $ / shares

12 Months Ended

Apr. 26, 2018

Apr. 23, 2015

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Stock Compensation Plan [Member]

Stock-Based Compensation

Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized

5,500,000

Shares available for grant

Shares available, at the beginning of the year

5,051,147

7,305,368

11,173,545

Stock options granted (in shares)

(711,479)

(558,426)

(500,000)

Stock options forfeited (in shares)

877,803

1,978,042

1,081,107

Stock options expired under former plans (in shares)

(412,467)

Nonvested equity stock and stock units granted (in shares)

^[2]

(4,993,802)

^[1]

(5,007,947)

^[3]

(5,316,675)

Nonvested equity stock and stock units forfeited (in shares)

^[2]

4,350,377

1,334,110

1,279,858

Shares available, at the end of the period

10,074,046.000

5,051,147

7,305,368

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)

525,965

394,853

300,003

Options

Shares available for grant

Stock options granted (in shares)

(711,479)

(558,426)

(500,000)

Stock options forfeited (in shares)

877,803

1,978,042

1,081,107

Options granted (in dollars per share)

$ 12.84

$ 12.95

$ 12.29

Expected weighted-average period for recognition of compensation cost (in years)

2 years 9 months

Employee Stock [Member]

Stock-Based Compensation

Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized

2,000,000

2,000,000

Shares available for grant

Shares available, at the end of the period

2,294,878

Expected weighted-average period for recognition of compensation cost (in years)

4 months

[1]	Amount includes 394,853 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 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.

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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.

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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.

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Number of additional shares authorized for issuance under an established share-based compensation plan.

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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.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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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.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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