Income Taxes	3 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes ProAssurance estimates its annual effective tax rate at the end of each quarterly reporting period and uses this estimated rate to record the provision for income taxes in the interim financial statements. The provision for income taxes is different from that which would be obtained by applying the statutory federal income tax rate to income before income taxes primarily because a portion of ProAssurance’s investment income is tax-exempt, and because ProAssurance utilizes tax credit benefits transferred from tax credit partnership investments. In addition, ProAssurance's provision for income taxes in 2018 was impacted by certain provisions of the TCJA, as discussed below. ProAssurance had a total liability for federal and U.K. income taxes of $6.3 million at March 31, 2018 and $8.0 million at December 31, 2017, both carried as a part of other liabilities. The liability for unrecognized tax benefits, which is included in the total liability for federal and U.K. income taxes, was $5.2 million and $5.8 million at March 31, 2018 and December 31, 2017, respectively, which included an accrued liability for interest of approximately $0.6 million and $0.5 million, respectively. Tax Cuts and Jobs Act The TCJA was signed into law on December 22, 2017 and contains several key provisions that impact the Company's business, including the reduction of the U.S. federal corporate tax rate from 35% to 21% effective January 1, 2018, the reduction in the amount of executive compensation that could qualify as a tax deduction, a minimum tax on payments made to related foreign entities and a change in how property and casualty taxpayers discount loss reserves. Effective January 1, 2018, the TCJA introduced a minimum tax on payments made to related foreign entities referred to as the BEAT. The BEAT is imposed by adding back into the U.S. tax base any base erosion payment made by the U.S. taxpayer to a related foreign entity and applying a minimum tax rate to this newly calculated modified taxable income. Base erosion payments represent any amount paid or accrued by the U.S. taxpayer to a related foreign entity for which a deduction is allowed. Premiums the Company cedes to the SPCs at its newly formed wholly owned Cayman Islands reinsurance subsidiary, Inova Re, do not fall within the scope of base erosion payments as the SPCs at Inova Re intend to elect to be taxed as U.S. taxpayers. However, premiums the Company cedes to the one active SPC at its wholly owned Cayman Islands reinsurance subsidiary, Eastern Re, fall within the scope of base erosion payments and therefore could be significantly impacted by the BEAT. See further discussion on the Company’s new subsidiary, Inova Re, and its Cayman Islands SPC operations in Note 12. Management has evaluated its exposure to the BEAT and has concluded that the Company’s outbound deductible payments to related foreign entities are below the threshold for application of the BEAT; therefore, ProAssurance has not recognized any incremental tax expense for the BEAT provision of the TCJA for the three months ended March 31, 2018. ProAssurance was able to complete its accounting for all areas of the TCJA during the period of enactment except as described below. Provisional amount As noted in ProAssurance's December 31, 2017 Form 10-K, ProAssurance was able to make a reasonable estimate of the effects on its existing deferred tax asset balances at December 31, 2017 as it relates to the limitation on the future deductibility of certain executive compensation and recorded a provisional charge to income tax expense from continuing operations for the year ended December 31, 2017. As of March 31, 2018, ProAssurance has not made any measurement-period adjustments to this provisional amount and any future guidance from the IRS addressing the effects of the TCJA on executive compensation could result in a material change to this provisional amount. Provisional amount not reasonably estimable As noted in ProAssurance's December 31, 2017 Form 10-K, ProAssurance was unable to reasonably estimate the impact of the change in loss reserve discounting factors due to the TCJA; therefore, no provisional amount was recorded at December 31, 2017. As of March 31, 2018, the IRS has yet to release the 2018 discount factors; therefore, ProAssurance has not adjusted its deferred tax balances due to the enactment of the TCJA. ProAssurance continues to utilize the discount factors based on existing accounting guidance and the provisions of the tax laws that were in effect immediately prior to enactment of the TCJA. Once the IRS releases the 2018 loss reserve discount factors, ProAssurance will complete its analysis and include the effect of the difference in the reserve discount factors in the period the analysis is complete or the impact is reasonably estimable.

Income Taxes

ProAssurance estimates its annual effective tax rate at the end of each quarterly reporting period and uses this estimated rate to record the provision for income taxes in the interim financial statements. The provision for income taxes is different from that which would be obtained by applying the statutory federal income tax rate to income before income taxes primarily because a portion of ProAssurance’s investment income is tax-exempt, and because ProAssurance utilizes tax credit benefits transferred from tax credit partnership investments. In addition, ProAssurance's provision for income taxes in 2018 was impacted by certain provisions of the TCJA, as discussed below.

ProAssurance had a total liability for federal and U.K. income taxes of $6.3 million at March 31, 2018 and $8.0 million at December 31, 2017, both carried as a part of other liabilities. The liability for unrecognized tax benefits, which is included in the total liability for federal and U.K. income taxes, was $5.2 million and $5.8 million at March 31, 2018 and December 31, 2017, respectively, which included an accrued liability for interest of approximately $0.6 million and $0.5 million, respectively.

Tax Cuts and Jobs Act

The TCJA was signed into law on December 22, 2017 and contains several key provisions that impact the Company's business, including the reduction of the U.S. federal corporate tax rate from 35% to 21% effective January 1, 2018, the reduction in the amount of executive compensation that could qualify as a tax deduction, a minimum tax on payments made to related foreign entities and a change in how property and casualty taxpayers discount loss reserves.

Effective January 1, 2018, the TCJA introduced a minimum tax on payments made to related foreign entities referred to as the BEAT. The BEAT is imposed by adding back into the U.S. tax base any base erosion payment made by the U.S. taxpayer to a related foreign entity and applying a minimum tax rate to this newly calculated modified taxable income. Base erosion payments represent any amount paid or accrued by the U.S. taxpayer to a related foreign entity for which a deduction is allowed. Premiums the Company cedes to the SPCs at its newly formed wholly owned Cayman Islands reinsurance subsidiary, Inova Re, do not fall within the scope of base erosion payments as the SPCs at Inova Re intend to elect to be taxed as U.S. taxpayers. However, premiums the Company cedes to the one active SPC at its wholly owned Cayman Islands reinsurance subsidiary, Eastern Re, fall within the scope of base erosion payments and therefore could be significantly impacted by the BEAT. See further discussion on the Company’s new subsidiary, Inova Re, and its Cayman Islands SPC operations in Note 12. Management has evaluated its exposure to the BEAT and has concluded that the Company’s outbound deductible payments to related foreign entities are below the threshold for application of the BEAT; therefore, ProAssurance has not recognized any incremental tax expense for the BEAT provision of the TCJA for the three months ended March 31, 2018.

ProAssurance was able to complete its accounting for all areas of the TCJA during the period of enactment except as described below.

Provisional amount

As noted in ProAssurance's December 31, 2017 Form 10-K, ProAssurance was able to make a reasonable estimate of the effects on its existing deferred tax asset balances at December 31, 2017 as it relates to the limitation on the future deductibility of certain executive compensation and recorded a provisional charge to income tax expense from continuing operations for the year ended December 31, 2017. As of March 31, 2018, ProAssurance has not made any measurement-period adjustments to this provisional amount and any future guidance from the IRS addressing the effects of the TCJA on executive compensation could result in a material change to this provisional amount.

Provisional amount not reasonably estimable

As noted in ProAssurance's December 31, 2017 Form 10-K, ProAssurance was unable to reasonably estimate the impact of the change in loss reserve discounting factors due to the TCJA; therefore, no provisional amount was recorded at December 31, 2017. As of March 31, 2018, the IRS has yet to release the 2018 discount factors; therefore, ProAssurance has not adjusted its deferred tax balances due to the enactment of the TCJA. ProAssurance continues to utilize the discount factors based on existing accounting guidance and the provisions of the tax laws that were in effect immediately prior to enactment of the TCJA. Once the IRS releases the 2018 loss reserve discount factors, ProAssurance will complete its analysis and include the effect of the difference in the reserve discount factors in the period the analysis is complete or the impact is reasonably estimable.