The Company discounts its liabilities for certain workers’ compensation reserves. The amount of workers’ compensation reserves that were discounted was $1,655 million and $1,731 million at December 31, 2020 and 2019, respectively. The aggregate net discount for those reserves, after reflecting the effects of ceded reinsurance, was $483 million and $530 million at December 31, 2020 and 2019, respectively. At December 31, 2020, discount rates by year ranged from 0.7% to 6.5%, with a weighted average discount rate of 3.6%. Substantially all discounted workers’ compensation reserves (97% of total discounted reserves at December 31, 2020) are excess workers’ compensation reserves. In order to properly match loss expenses with income earned on investment securities supporting the liabilities, reserves for excess workers’ compensation business are discounted using risk-free discount rates determined by reference to the U.S. Treasury yield curve. These rates are determined annually based on the weighted average rate for the period. Once established, no adjustments are made to the discount rate for that period, and any increases or decreases in loss reserves in subsequent years are discounted at the same rate, without regard to when any such adjustments are recognized. The expected loss and loss expense payout patterns subject to discounting are derived from the Company’s loss payout experience. The Company also discounts reserves for certain other long-duration workers’ compensation reserves (representing approximately 3% of total discounted reserves at December 31, 2020), including reserves for quota share reinsurance and reserves related to losses regarding occupational lung disease. These reserves are discounted at statutory rates permitted by the Department of Insurance of the State of Delaware. To date, known environmental and asbestos claims have not had a material impact on the Company’s operations, because its subsidiaries generally did not insure large industrial companies that are subject to significant environmental or asbestos exposures prior to 1986 when an absolute exclusion was incorporated into standard policy language. The Company’s net reserves for losses and loss expenses relating to environmental and asbestos claims on policies written before adoption of the absolute exclusion was $19 million at December 31, 2020 and $24 million at December 31, 2019. The estimation of these liabilities is subject to significantly greater than normal variation and uncertainty because it is difficult to make an actuarial estimate of these liabilities due to the absence of a generally accepted actuarial methodology for these exposures and the potential effect of significant unresolved legal matters, including coverage issues, as well as the cost of litigating the legal issues. Additionally, the determination of ultimate damages and the final allocation of such damages to financially responsible parties are highly uncertain. The table below provides a reconciliation of the beginning of year and end of year property casualty reserves for the indicated years: (In thousands) 2020 2019 2018 Net reserves at beginning of year $ 10,697,998  $ 10,248,883  $ 10,056,914  Cumulative effect adjustment resulting from changes in accounting principles (1) 5,927  —  —  Restated net reserves at beginning of period 10,703,925  10,248,883  10,056,914  Net provision for losses and loss expenses: Claims occurring during the current year (2) 4,432,937  4,057,989  3,926,489  Increase in estimates for claims occurring in prior years (3) 627  34,079  6,831  Loss reserve discount amortization 35,142  39,048  41,382  Total 4,468,706  4,131,116  3,974,702  Net payments for claims: Current year 921,054  985,599  964,808  Prior years 2,677,595  2,673,803  2,700,077  Total 3,598,649  3,659,402  3,664,885  Foreign currency translation 46,411  (22,599) (117,848) Net reserves at end of year 11,620,393  10,697,998  10,248,883  Ceded reserves at end of year 2,164,037  1,885,251  1,717,565  Gross reserves at end of year $ 13,784,430  $ 12,583,249  $ 11,966,448  Net change in premiums and losses occurring in prior years: Increase in estimates for claims occurring in prior years (3) $ (627) $ (34,079) $ (6,831) Retrospective premium adjustments for claims occurring in prior years (4) 16,807  53,511  45,638  Net favorable premium and reserve development on prior years $ 16,180  $ 19,432  $ 38,807  11