| **Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands**                                                                                                                                      | 3 Months Ended |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|
||
| **Consolidated Statements Of Comprehensive Income [Abstract]**                                                                                                                                                    |                |   |   |
| Net income                                                                                                                                                                                                        |                | $ 51,737 | $ 48,545 |
| **Other comprehensive income, net of tax:**                                                                                                                                                                       |                |   |   |
| Unrealized holding (loss) gain on investments, net of tax (benefit) expense of $(4) and $41 for the three months ended March 31, 2016 and 2015, respectively                                                      |                | (6) | $ 75 |
| Reclassification of gain on sale of investment to net income, net of tax of $30 for the three months ended March 31, 2016                                                                                         | [1]            | (57) |  |
| Comprehensive income                                                                                                                                                                                              |                | $ 51,674 | $ 48,620 |
|                                                                                                                                                                                                                   |
| [1]Amount of pre-tax gain of $87 reclassified from accumulated other comprehensive income to gain on sale of other assets on the consolidated statements of net income for the three months ended March 31, 2016. |

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| - Definition
Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.
+ References
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| - Definition
The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.
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| - Definition
Amount after tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.
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| - Definition
Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.
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| - References
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