| New Accounting Pronouncements or Change in Accounting Principle [Line Items] | |
| Other operating expenses | 51.02M |
| Income tax expense | 766K |
| Net income attributable to Tower Group, Inc. | -48.74M |
| Earnings per share attributable to Tower Group, Inc. | |
| Basic | -0.85 |
| Diluted | -0.85 |
| New Accounting Pronouncements or Change in Accounting Principle [Line Items] | |
| Other operating expenses | |
| Income tax expense | |
| Net income attributable to Tower Group, Inc. | |
| Earnings per share attributable to Tower Group, Inc. | |
| Basic | |
| Diluted | |
| New Accounting Pronouncements or Change in Accounting Principle [Line Items] | |
| Other operating expenses | |
| Income tax expense | |
| Net income attributable to Tower Group, Inc. | |
| Earnings per share attributable to Tower Group, Inc. | |
| Basic | |
| Diluted | |