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Cash, Cash Equivalents and Restricted Cash (Details) (USD $)
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Mar. 31, 2015
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Dec. 31, 2014
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|---|---|---|
| Cash, Cash Equivalents and Restricted Cash | ||
| Cash and cash equivalents | $ 330,438,000 | $ 521,195,000 |
| Restricted cash deposits kept as collateral for outstanding letters of credit | 28,000,000 | 33,800,000 |
| Restricted cash | ||
| Restricted cash | 29,059,000 | 35,720,000 |
| RMC | ||
| Restricted cash | ||
| Restricted cash | $ 1,100,000 | $ 1,900,000 |