| Underwriting results of reportable segments [Table Text Block] |
| The following tables summarize the underwriting results of our reportable segments, as well as the carrying values of allocated goodwill and intangible assets: | | | | | | | | | | | | | | | | | | | | | | | At and year ended December 31, 2011 | | Insurance | | Reinsurance | | Total | | | | | | | | | | | | | | | | | | | Gross premiums written | $ | 2,121,829 | | $ | 1,974,324 | | $ | 4,096,153 | | | | Net premiums written | | 1,466,134 | | | 1,953,300 | | | 3,419,434 | | | | Net premiums earned | | 1,429,687 | | | 1,885,274 | | | 3,314,961 | | | | Other insurance related income | | 2,396 | | | - | | | 2,396 | | | | Net losses and loss expenses | | (919,319) | | | (1,755,733) | | | (2,675,052) | | | | Acquisition costs | | (199,583) | | | (387,886) | | | (587,469) | | | | General and administrative expenses | | (278,147) | | | (103,915) | | | (382,062) | | | | Underwriting income (loss) | $ | 35,034 | | $ | (362,260) | | | (327,226) | | | | | | | | | | | | | | | | | | | Corporate expenses | | | | | | | | | | (77,089) | | | | Net investment income | | | | | | | | | | 362,430 | | | | Net realized investment gains | | | | | | | | | | 121,439 | | | | Foreign exchange gains | | | | | | | | | | 44,582 | | | | Interest expense and financing costs | | | | | | | | | | (62,598) | | | | Income before income taxes | | | | | | | | | $ | 61,538 | | | | | | | | | | | | | | | | | | | Net loss and loss expense ratio | | 64.3 | % | | | 93.1 | % | | | 80.7 | % | | | | Acquisition cost ratio | | 14.0 | % | | | 20.6 | % | | | 17.7 | % | | | | General and administrative expense ratio | | 19.4 | % | | | 5.5 | % | | | 13.9 | % | | | | Combined ratio | | 97.7 | % | | | 119.2 | % | | | 112.3 | % | | | | | | | | | | | | | | | | | | | Goodwill and intangible assets | $ | 99,590 | | $ | - | | $ | 99,590 | | | | | | | | | | | | | | | | |
| | | | | | | At and year ended December 31, 2010 | | Insurance | | Reinsurance | | Total | | | | | | | | | | | | | | | | | | | Gross premiums written | $ | 1,916,116 | | $ | 1,834,420 | | $ | 3,750,536 | | | | Net premiums written | | 1,332,220 | | | 1,815,320 | | | 3,147,540 | | | | Net premiums earned | | 1,206,493 | | | 1,740,917 | | | 2,947,410 | | | | Other insurance related income | | 2,073 | | | - | | | 2,073 | | | | Net losses and loss expenses | | (569,869) | | | (1,107,263) | | | (1,677,132) | | | | Acquisition costs | | (152,223) | | | (336,489) | | | (488,712) | | | | General and administrative expenses | | (276,435) | | | (98,001) | | | (374,436) | | | | Underwriting income | $ | 210,039 | | $ | 199,164 | | | 409,203 | | | | | | | | | | | | | | | | | | | Corporate expenses | | | | | | | | | | (75,449) | | | | Net investment income | | | | | | | | | | 406,892 | | | | Net realized investment gains | | | | | | | | | | 195,098 | | | | Foreign exchange gains | | | | | | | | | | 15,535 | | | | Interest expense and financing costs | | | | | | | | | | (55,876) | | | | Income before income taxes | | | | | | | | | $ | 895,403 | | | | | | | | | | | | | | | | | | | Net loss and loss expense ratio | | 47.2 | % | | | 63.6 | % | | | 56.9 | % | | | | Acquisition cost ratio | | 12.6 | % | | | 19.3 | % | | | 16.6 | % | | | | General and administrative expense ratio | | 23.0 | % | | | 5.7 | % | | | 15.2 | % | | | | Combined ratio | | 82.8 | % | | | 88.6 | % | | | 88.7 | % | | | | | | | | | | | | | | | | | | | Goodwill and intangible assets | $ | 103,231 | | $ | - | | $ | 103,231 | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | At and year ended December 31, 2009 | | Insurance | | Reinsurance | | Total | | | | | | | | | | | | | | | | | | | Gross premiums written | $ | 1,775,590 | | $ | 1,811,705 | | $ | 3,587,295 | | | | Net premiums written | | 1,025,061 | | | 1,791,368 | | | 2,816,429 | | | | Net premiums earned | | 1,157,966 | | | 1,633,798 | | | 2,791,764 | | | | Other insurance related income (loss) | | (130,946) | | | 1,265 | | | (129,681) | | | | Net losses and loss expenses | | (612,694) | | | (811,178) | | | (1,423,872) | | | | Acquisition costs | | (113,187) | | | (307,308) | | | (420,495) | | | | General and administrative expenses | | (216,954) | | | (76,127) | | | (293,081) | | | | Underwriting income | $ | 84,185 | | $ | 440,450 | | | 524,635 | | | | | | | | | | | | | | | | | | | Corporate expenses | | | | | | | | | | (77,076) | | | | Net investment income | | | | | | | | | | 464,478 | | | | Net realized investment losses | | | | | | | | | | (311,584) | | | | Foreign exchange losses | | | | | | | | | | (28,561) | | | | Interest expense and financing costs | | | | | | | | | | (32,031) | | | | Income before income taxes | | | | | | | | | $ | 539,861 | | | | | | | | | | | | | | | | | | | Net loss and loss expense ratio | | 52.9 | % | | | 49.6 | % | | | 51.0 | % | | | | Acquisition cost ratio | | 9.8 | % | | | 18.8 | % | | | 15.1 | % | | | | General and administrative expense ratio | | 18.7 | % | | | 4.7 | % | | | 13.2 | % | | | | Combined ratio | | 81.4 | % | | | 73.1 | % | | | 79.3 | % | | | | | | | | | | | | | | | | | | | Goodwill and intangible assets | $ | 91,505 | | $ | - | | $ | 91,505 | | | | | | | | | | | | | | | | |
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| Net premiums earned by segment and line of business [Table Text Block] |
| The following table presents our net premiums earned by segment and line of business: | | | | | | | | | | | | | | | | | | | | | | | | | | | Year ended December 31, | 2011 | | 2010 | | 2009 | | | | | | | | | | | | | | | | Insurance | | | | | | | | | | | | Property | $ | 385,291 | | $ | 337,525 | | $ | 268,469 | | | | Marine | | 152,123 | | | 145,356 | | | 139,196 | | | | Terrorism | | 35,213 | | | 32,486 | | | 34,001 | | | | Aviation | | 70,681 | | | 66,636 | | | 64,245 | | | | Credit and political risk | | 97,680 | | | 89,773 | | | 188,311 | | | | Professional lines | | 536,238 | | | 444,663 | | | 381,364 | | | | Liability | | 89,555 | | | 87,481 | | | 82,380 | | | | Accident & health | | 62,906 | | | 2,573 | | | - | | | | Total Insurance | | 1,429,687 | | | 1,206,493 | | | 1,157,966 | | | | | | | | | | | | | | | | Reinsurance | | | | | | | | | | | | Catastrophe | | 456,858 | | | 454,954 | | | 451,085 | | | | Property | | 356,022 | | | 323,201 | | | 311,272 | | | | Professional lines | | 281,025 | | | 285,224 | | | 266,792 | | | | Credit and bond | | 263,912 | | | 217,809 | | | 179,362 | | | | Motor | | 202,830 | | | 127,404 | | | 99,497 | | | | Liability | | 230,872 | | | 232,014 | | | 227,511 | | | | Engineering | | 65,727 | | | 71,229 | | | 66,428 | | | | Other | | 28,028 | | | 29,082 | | | 31,851 | | | | Total Reinsurance | | 1,885,274 | | | 1,740,917 | | | 1,633,798 | | | | | | | | | | | | | | | | Total | $ | 3,314,961 | | $ | 2,947,410 | | $ | 2,791,764 | | | | | | | | | | | | | |
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