Investments	12 Months Ended
Investments	Dec. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
Investments	INVESTMENTS In August 2007 and December 2008, the Company made an aggregate investment of $7.5 million in kaleo, Inc. (“kaléo”), a privately held specialty pharmaceutical company dedicated to building innovative solutions for serious and life-threatening medical conditions. Tredegar owns Series A-3 Preferred Stock and Series B Preferred Stock in kaléo that, taken together, represents on a fully-diluted basis an approximate 20% interest in kaléo. Tredegar accounts for its investment in kaléo under the fair value option. At the time of the initial investment, the Company elected the fair value option of accounting since its investment objectives were similar to those of venture capitalists, which typically do not have controlling financial interests. kaléo’s stock is not publicly traded. The estimated fair value of the Company’s investment was $34.6 million as of December 31, 2020 and $95.5 million as of December 31, 2019. The Company recognized a pre-tax loss on its investment in kaléo of $60.9 million ($47.6 million after taxes) in 2020, which was primarily due to: (i) current projections that assume ongoing pricing pressures, (ii) expected changes in market access as well as continued lower market demand for epinephrine delivery devices resulting from COVID-19-driven delays in in-person back-to-school schedules and social distancing guidelines, and (iii) a higher private company liquidity discount. The net appreciation on its investment of $28.5 million ($23.4 million after taxes) in 2019 included a pre-tax cash dividend of $17.6 million received on April 30, 2019. Future dividends are subject to the discretion of kaléo’s board of directors. Amounts recognized associated with the Company’s investment in kaléo are included in “Other income (expense), net” in the consolidated statements of income and separately stated in the EBITDA from ongoing operations table in Note 5. The Company estimates the fair value of its investment in kaléo by: (i) computing the weighted average estimated enterprise value (“EV”) utilizing both the discounted cash flow method (the “DCF Method”) and the application of a market multiple to earnings before interest, taxes, depreciation and amortization (the “EBITDA Multiple Method”), (ii) applying adjustments for any surplus or deficient working capital and estimates of contingent liabilities, (iii) adding cash and cash equivalents, (iv) subtracting interest-bearing debt, (v) subtracting a private company liquidity discount estimated at 20% at December 31, 2020 (versus 10% at December 31, 2019) of the net result of (i) through (iv), and (vi) applying liquidation preferences and fully diluted ownership percentages to the estimated equity value computed in (i) through (v). The Company’s estimate of kaléo’s EV as of December 31, 2020 was determined by weighting the EBITDA Multiple Method by 20% and the DCF Method by 80% compared to an 80% and 20% weighting of the EBITDA Multiple Method and DCF Method, respectively, used in the Company's estimate of kaléo’s EV as of December 31, 2019. A heavier weighting towards the DCF Method as of December 31, 2020 was used since kaléo’s projections better reflect ongoing pricing pressures and expected changes in market access. The DCF Method projections rely on numerous assumptions and Level 3 inputs. In addition, there are various regulatory and legal enforcement efforts, including an ongoing Department of Justice investigation related to kaléo’s discontinued Evzio business, which could have a material adverse effect on kaléo’s business that require assessment in any valuation method applied.The ultimate value of the Company’s ownership interest in kaléo will be determined and realized only if and when a liquidity event occurs, and the ultimate value could be materially different from the $34.6 million estimated fair value reflected in the Company’s financial statements at December 31, 2020.