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Fair Value Disclosures (Details 1) (USD $)
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Jun. 30, 2014
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Dec. 31, 2013
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|---|---|---|
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4.50% senior notes due two thousand eighteen [Member] | Level 2 [Member]
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| Fair value of fixed-rate debt | ||
| Aggregate Principal | $ 175,000,000 | $ 175,000,000 |
| Estimated Fair Value | 179,813,000 | 174,125,000 |
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7.15% senior notes due 2020 [Member] | Level 2 [Member]
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| Fair value of fixed-rate debt | ||
| Aggregate Principal | 300,000,000 | 300,000,000 |
| Estimated Fair Value | 334,500,000 | 325,500,000 |
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7.00% senior notes due 2022 [Member] | Level 2 [Member]
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||
| Fair value of fixed-rate debt | ||
| Aggregate Principal | 300,000,000 | 300,000,000 |
| Estimated Fair Value | 330,390,000 | 318,750,000 |
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1.875% convertible senior notes due 2032 [Member]
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| Fair value of fixed-rate debt | ||
| Aggregate Principal | 1,000 | |
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1.875% convertible senior notes due 2032 [Member] | Level 2 [Member]
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| Fair value of fixed-rate debt | ||
| Aggregate Principal | 126,500,000 | 126,500,000 |
| Estimated Fair Value | $ 132,667,000 | $ 142,154,000 |