| **Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands**                                                                                                                                          | 3 Months Ended | 9 Months Ended |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Consolidated Statements Of Comprehensive Income [Abstract]**                                                                                                                                                        |                |           |   |   |   |
| Net income attributable to common shareholders                                                                                                                                                                        |                | $ 67,429       | $ 67,996 | $ 173,356 | $ 166,424 |
| **Other comprehensive income, net of tax:**                                                                                                                                                                           |                |           |   |   |   |
| Unrealized holding (loss) gain on investments, net of tax (benefit) expense of $(120) and $(33) for the three months and $(90) and $73 for the nine months ended September 30, 2015 and 2014, respectively            |                | $ (223)        | $ (62) | $ (169) | 136 |
| Reclassification adjustment for loss reported in net income, net of tax benefit of $134 for the nine months ended September 30, 2014                                                                                  | [1]            |                |  |  | 249 |
| Comprehensive income                                                                                                                                                                                                  |                | $ 67,206       | $ 67,934 | $ 173,187 | $ 166,809 |
|                                                                                                                                                                                                                       |
| [1]Amount of pre-tax loss of $383 reclassified from accumulated other comprehensive income to loss on sale of other assets on the consolidated statements of net income for the nine months ended September 30, 2014. |

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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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