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Employee Benefit Plans (Details) (USD $)
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12 Months Ended |
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Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2012
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| Defined Benefit Plan Disclosure [Line Items] |
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| Maximum annual contributions |
$ 17,500 |
$ 17,500 |
$ 17,000 |
| Employer's matching contribution |
100.00% |
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| Percentage of employee eligible earnings matched |
1.00% |
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| Additional employer's matching contribution |
50.00% |
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| Participant contributions, vested percentage |
100.00% |
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| Company contributions |
$ 9,000,000 |
$ 7,000,000 |
$ 4,900,000 |
| Minimum |
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| Defined Benefit Plan Disclosure [Line Items] |
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| Additional percentage of employee eligible earnings matched |
2.00% |
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| Maximum |
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| Defined Benefit Plan Disclosure [Line Items] |
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| Additional percentage of employee eligible earnings matched |
6.00% |
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| One Year of Service |
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| Defined Benefit Plan Disclosure [Line Items] |
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| Employer contributions, vested percentage |
20.00% |
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| Employer contributions, requisite service period for vesting |
1 year |
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| Two Years of Service |
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| Defined Benefit Plan Disclosure [Line Items] |
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| Employer contributions, vested percentage |
100.00% |
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| Employer contributions, requisite service period for vesting |
2 years |
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