Summary of Significant Accounting Policies - Restricted Cash, Cash Equivalents and Investments (Details)
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12 Months Ended |
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Dec. 31, 2013
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Minimum
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Restricted Cash and Cash Equivalents Items [Line Items] | |
U.S. Treasury Security Maturity Term | 6 months |
Maximum
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Restricted Cash and Cash Equivalents Items [Line Items] | |
U.S. Treasury Security Maturity Term | 12 months |