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Summary of Significant Accounting Policies (Details) (USD $)
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12 Months Ended | ||
|---|---|---|---|
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Dec. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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| Revenue Recognition | |||
| Number of Reportable Segments | 1 | 1 | |
| Number of principal sources from where revenue is derived | 3 | ||
| Future minimum payments for operating leases | $ 27,712,000 | ||
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CDP Agreement
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| Revenue Recognition | |||
| Operating lease income recorded in CDP and services revenue | 6,900,000 | 9,700,000 | 5,400,000 |
| Future minimum payments for operating leases | $ 800,000 | $ 8,400,000 | |