Income Taxes	6 Months Ended
Apr. 01, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes In the second quarter and first six months of 2017, our effective tax rate was (5)% on a pre-tax loss of $1.1 million, and (36)% on a pre-tax loss of $7.6 million, respectively, compared to (45)% on pre-tax loss of $3.6 million and (26)% on a pre-tax loss $23.1 million in the second quarter and first six months of 2016, respectively. In the second quarter and first six months of 2017 and 2016, our effective tax rate was lower than the 35% statutory federal income tax rate due to our corporate structure in which our foreign taxes are at a net effective tax rate lower than the U.S. rate. A significant amount of our foreign earnings is generated by our subsidiaries organized in Ireland. In 2017 and 2016, the foreign rate differential predominantly relates to these Irish earnings. Our foreign rate differential in 2017 and 2016 includes the continuing rate benefit from a business realignment completed on September 30, 2014 in which intellectual property was transferred between two wholly-owned foreign subsidiaries. For the second quarter and first six months of 2017 and 2016, this realignment resulted in tax benefits of approximately $4 million, and $12 million and $4 million and $7 million, respectively. Also, in the second quarter and first six months of 2017, we recorded a tax benefit of $1.8 million related to a favorable agreement in a foreign jurisdiction. Additionally, in the first six months of 2016, our provision reflects a tax benefit of $2.6 million related to a retroactive extension of the U.S. research and development tax credit enacted in the first quarter of 2016. This benefit was offset by a corresponding provision to increase our U.S. valuation allowance. We have concluded, based on the weight of available evidence, that a full valuation allowance continues to be required against our U.S. net deferred tax assets as they are not more likely than not to be realized in the future. We will continue to reassess our valuation allowance requirements each financial reporting period. In the normal course of business, PTC and its subsidiaries are examined by various taxing authorities, including the Internal Revenue Service in the U.S. We regularly assess the likelihood of additional assessments by tax authorities and provide for these matters as appropriate. We are currently under audit by tax authorities in several jurisdictions. Audits by tax authorities typically involve examination of the deductibility of certain permanent items, limitations on net operating losses and tax credits. Although we believe our tax estimates are appropriate, the final determination of tax audits and any related litigation could result in material changes in our estimates. As of April 1, 2017 and September 30, 2016, we had unrecognized tax benefits of $14.3 million and $15.5 million, respectively. If all of our unrecognized tax benefits as of April 1, 2017 were to become recognizable in the future, we would record a benefit to the income tax provision of $12.6 million, which would be partially offset by an increase in the U.S. valuation allowance of $5.1 million. Although we believe our tax estimates are appropriate, the final determination of tax audits and any related litigation could result in favorable or unfavorable changes in our estimates. We believe it is reasonably possible that within the next 12 months the amount of unrecognized tax benefits related to the resolution of multi-jurisdictional tax positions could be reduced by up to $6 million as audits close and statutes of limitations expire. In the fourth quarter of 2016, we received an assessment of approximately $12 million from the tax authorities in Korea related to a tax audit. The assessment relates to various tax issues but primarily to foreign withholding taxes. We have appealed and will vigorously defend our positions. We believe that it is more likely than not that our positions will be sustained upon appeal. Accordingly, we have not recorded a tax reserve for this matter. We paid this assessment in the first quarter of 2017 and have recorded the amount in other assets, pending resolution of the appeal.

Income Taxes

In the second quarter and first six months of 2017, our effective tax rate was (5)% on a pre-tax loss of $1.1 million, and (36)% on a pre-tax loss of $7.6 million, respectively, compared to (45)% on pre-tax loss of $3.6 million and (26)% on a pre-tax loss $23.1 million in the second quarter and first six months of 2016, respectively. In the second quarter and first six months of 2017 and 2016, our effective tax rate was lower than the 35% statutory federal income tax rate due to our corporate structure in which our foreign taxes are at a net effective tax rate lower than the U.S. rate. A significant amount of our foreign earnings is generated by our subsidiaries organized in Ireland. In 2017 and 2016, the foreign rate differential predominantly relates to these Irish earnings. Our foreign rate differential in 2017 and 2016 includes the continuing rate benefit from a business realignment completed on September 30, 2014 in which intellectual property was transferred between two wholly-owned foreign subsidiaries. For the second quarter and first six months of 2017 and 2016, this realignment resulted in tax benefits of approximately $4 million, and $12 million and $4 million and $7 million, respectively. Also, in the second quarter and first six months of 2017, we recorded a tax benefit of $1.8 million related to a favorable agreement in a foreign jurisdiction. Additionally, in the first six months of 2016, our provision reflects a tax benefit of $2.6 million related to a retroactive extension of the U.S. research and development tax credit enacted in the first quarter of 2016. This benefit was offset by a corresponding provision to increase our U.S. valuation allowance.

We have concluded, based on the weight of available evidence, that a full valuation allowance continues to be required against our U.S. net deferred tax assets as they are not more likely than not to be realized in the future. We will continue to reassess our valuation allowance requirements each financial reporting period.

In the normal course of business, PTC and its subsidiaries are examined by various taxing authorities, including the Internal Revenue Service in the U.S. We regularly assess the likelihood of additional assessments by tax authorities and provide for these matters as appropriate. We are currently under audit by tax authorities in several jurisdictions. Audits by tax authorities typically involve examination of the deductibility of certain permanent items, limitations on net operating losses and tax credits. Although we believe our tax estimates are appropriate, the final determination of tax audits and any related litigation could result in material changes in our estimates.

As of April 1, 2017 and September 30, 2016, we had unrecognized tax benefits of $14.3 million and $15.5 million, respectively. If all of our unrecognized tax benefits as of April 1, 2017 were to become recognizable in the future, we would record a benefit to the income tax provision of $12.6 million, which would be partially offset by an increase in the U.S. valuation allowance of $5.1 million.

Although we believe our tax estimates are appropriate, the final determination of tax audits and any related litigation could result in favorable or unfavorable changes in our estimates. We believe it is reasonably possible that within the next 12 months the amount of unrecognized tax benefits related to the resolution of multi-jurisdictional tax positions could be reduced by up to $6 million as audits close and statutes of limitations expire.

In the fourth quarter of 2016, we received an assessment of approximately $12 million from the tax authorities in Korea related to a tax audit. The assessment relates to various tax issues but primarily to foreign withholding taxes. We have appealed and will vigorously defend our positions. We believe that it is more likely than not that our positions will be sustained upon appeal. Accordingly, we have not recorded a tax reserve for this matter. We paid this assessment in the first quarter of 2017 and have recorded the amount in other assets, pending resolution of the appeal.