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Goodwill and Intangible Assets (Details Textual) (USD $)
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3 Months Ended | 6 Months Ended | 12 Months Ended | ||
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Jun. 30, 2012
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Jun. 30, 2011
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Jun. 30, 2012
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Jun. 30, 2011
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Dec. 31, 2011
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| Goodwill and Intangible Assets (Textual) [Abstract] | |||||
| Contract validity period | 12 years 10 months 24 days | 13 years 6 months | |||
| Amortization expenses of acquired intangible assets | $ 11,100,000 | $ 9,900,000 | $ 21,600,000 | $ 19,800,000 | |
| Goodwill and Intangible Assets (Additional Textual) [Abstract] | |||||
| Amortization expense | 11,100,000 | 9,900,000 | 21,600,000 | 19,800,000 | |
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Contractual Rights [Member]
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| Goodwill and Intangible Assets (Textual) [Abstract] | |||||
| Contract validity period | 3 years | ||||
| Intangible asset acquired, fair value | 5,000,000 | ||||
| Amortization expenses of acquired intangible assets | 252,000 | ||||
| Goodwill and Intangible Assets (Additional Textual) [Abstract] | |||||
| Amortization expense | $ 252,000 | ||||