| **Stockholders' Equity (Narratives) (Details) - USD ($)**           | 3 Months Ended  | 6 Months Ended |
|---------------------------------------------------------------------|-----------------|----------------|
||
| **Common Stock [Abstract]**                                         |            |           |   |   |
| Stock Repurchased and Retired During Period, Value                  |            |           | $ 20,532,000 | $ 36,939,000 |
| Restricted Stock [Member]                                           |            |           |   |   |
| **Share-based Compensation [Abstract]**                             |            |           |   |   |
| Unrecognized share-based compensation expense                       | $ 13,800,000    |           | $ 13,800,000 |   |
| Weighted average period for recognition of unvested shares          |            |           | 1 year 7 months 6 days |   |
| Common Stock - Class A [Member]                                     |            |           |   |   |
| **Common Stock [Abstract]**                                         |            |           |   |   |
| Stock Repurchased and Retired During Period, Value                  |            |           | $ 196,000 | $ 18,808,000 |
| **Share-based Compensation [Abstract]**                             |            |           |   |   |
| Number of shares authorized                                         | 15,700,000.0    |           | 15,700,000.0 |   |
| Maximum [Member] | Restricted Stock [Member]                        |            |           |   |   |
| **Share-based Compensation [Abstract]**                             |            |           |   |   |
| Vesting period                                                      |            |           | 3 years |   |
| Stock Option Plan Member [Member] | Restricted Stock [Member]       |            |           |   |   |
| **Share-based Compensation [Abstract]**                             |            |           |   |   |
| Granted (USD per share)                                             |            |           | $ 17.68 | $ 14.70 |
| Fair value of awards vesting during period                          |            |           | $ 4,300,000 | $ 4,900,000 |
| Stock Option Plan Member [Member] | Common Stock - Class A [Member] |            |           |   |   |
| **Share-based Compensation [Abstract]**                             |            |           |   |   |
| Number of shares available for grant                                | 1,600,000       |           | 1,600,000 |   |
| Stock Buyback Program [Member]                                      |            |           |   |   |
| **Common Stock [Abstract]**                                         |            |           |   |   |
| Amount authorized per quarter by Board for share repurchases        | $ 5,000,000     |           |   |   |
| Stock Repurchased and Retired During Period, Shares                 | 500,000         | 1,200,000      | 1,100,000 | 2,300,000 |
| Stock Repurchase Program, Remaining Authorized Repurchase Amount    | $ 86,000,000.00 |           | $ 86,000,000.00 |   |
| Stock Buyback Program [Member] | Common Stock - Class A [Member]    |            |           |   |   |
| **Common Stock [Abstract]**                                         |            |           |   |   |
| Stock Repurchased and Retired During Period, Value                  | $ 8,300,000     | $ 19,700,000   | 19,500,000 | $ 35,900,000 |
| Other Nonoperating Income (Expense) [Member]                        |            |           |   |   |
| **Share-based Compensation [Abstract]**                             |            |           |   |   |
| Share-based compensation expense                                    |            |           | $ 5,000,000 | $ 5,300,000 |

| X                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount Authorized Per Quarter By Board For Share Repurchases
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| - Definition
Common Stock [Abstract]
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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
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Unrecognized cost of unvested share-based compensation awards.
+ References
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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.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
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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
Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).
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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.
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| - Definition
Amount remaining of a stock repurchase plan authorized.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of shares that have been repurchased and retired during the period.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).
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