Other operating costs. Other operating costs for the six months ended June 30, 2020 were $44.2 million, a decrease of $23.1 million, or 34.4%, from $67.3 million for the same period in the prior year. Other expenses decreased by $20.3 million due to the benefit associated with the recognition of $20.5 million in proceeds from Grants under the CARES Act included in Other operating costs, as discussed in the “Effects of the COVID-19 Pandemic” section. Travel and other expenses decreased $5.6 million due to cost mitigation efforts as a result of the COVID-19 pandemic. The decreases are offset by a $2.0 million increase in rent expense from new, renewed, and acquired leases and a $0.8 million increase in bad debt expense as compared to the same period in the prior year.
General and administrative expenses. General and administrative expenses for the six months ended June 30, 2020 were $60.2 million, an increase of $2.6 million, or 4.5%, from the same period in the prior year. The increase was primarily the result of incremental share-based compensation expense of $5.9 million recognized during the second quarter due to the modification of certain equity awards granted in 2017 and incentive compensation and other personnel-related costs increased by $2.2 million, offset by decreases in salary expense of $3.6 million and other expenses of $1.9 million as compared to the same period in the prior year.
Professional accounting and legal fees. Professional accounting and legal fees for the six months ended June 30, 2020 were $5.1 million, a decrease of $0.8 million, or 13.5%, from $5.9 million for the same period in the prior year primarily due to targeted efforts to remediate material weaknesses in our internal controls over financial reporting that occurred in the six months ended June 30, 2019 that did not recur in the same period of 2020.
Depreciation and amortization. Depreciation and amortization for the six months ended June 30, 2020 was $17.7 million, an increase of $0.2 million, or 1.0%, from the same period in the prior year. Amortization expense increased $0.9 million and depreciation expense decreased $0.7 million when compared to the same period in the prior year.
Interest expense, net. Interest expense for the six months ended June 30, 2020 decreased 0.7% to $16.9 million from $17.0 million for the same period in the prior year.
(Benefit) provision for income taxes. The benefit for income taxes for the six months ended June 30, 2020 was $2.8 million, or -22.8% of income before income taxes, compared to a provision of $0.7 million, or 18.0% of income before income taxes for the six months ended June 30, 2019. The effective tax rate in 2020 consisted principally of the 21% federal statutory tax rate, research and development tax credits, the rate impact from state income taxes, the shortfall from share-based compensation, and permanent tax differences. The decrease in the effective tax rate for the six months ended June 30, 2020 compared with the six months ended June 30, 2019 is primarily attributable to the recognition of research and development tax credits for the current and prior years in the current quarter, partially offset by a shortfall from share-based compensation.
We evaluate our deferred tax assets quarterly to determine whether adjustments to the valuation allowance are appropriate in light of changes in facts or circumstances, such as changes in expected future pre-tax earnings, tax law, interactions with taxing authorities, and developments in case law. Our material assumptions include forecasts of future pre-tax earnings and the nature and timing of future deductions and income represented by the deferred tax assets and liabilities, all of which involve the exercise of significant judgment. As of June 30, 2020, our valuation allowance approximated $2.1 million.
During the second quarter of 2020, we finalized a research and development study recognizing tax benefits of $2.1 million, net of tax reserves, related to the current year and $6.3 million, net of tax reserves, related to prior years. We recorded the tax benefit, before tax reserves, as a deferred tax asset in the second quarter of 2020.
The CARES Act, which was enacted on March 27, 2020, includes changes to certain tax laws related to the deductibility of interest expense and depreciation. ASC 740, Income Taxes, requires the effects of changes in tax rates and laws on deferred tax balances to be recognized in the period in which the legislation is enacted. This legislation had the effect of increasing our deferred income taxes and decreasing our current income taxes payable by approximately $5.4 million. The CARES Act allowed for bonus depreciation on certain types of qualified property and the provision for an increase in the amounts allowed for interest expense for tax years beginning January 1, 2019. We continue to evaluate other aspects of the CARES Act to determine whether other tax benefits are available.