Income Taxes	3 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes On December 22, 2017, the “Tax Cuts & Jobs Act” (hereafter referred to as “U.S. tax reform”) was signed into law and is effective for the Company starting in the quarter ended December 31, 2017. The TCJA provides for numerous significant tax law changes and modifications including the reduction of the U.S. federal corporate income tax rate from 35% to 21%, the requirement for companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously deferred and the creation of new taxes on certain foreign-sourced earnings. The impact on income taxes due to change in legislation is required under the authoritative guidance of Accounting Standards Codification (“ASC”) 740, Income Taxes, to be recognized in the period in which the law is enacted. In December 2017, the SEC staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (SAB 118), which allows the Company to record provisional amounts for the Tax Act during a measurement period not to extend beyond one year of the enactment date. The Company has recorded significant activity in the period of enactment due to the change in legislation. For the three months ended March 31, 2018, the Company did not have any significant adjustments to its provisional amounts previously recognized. However, in the current period, the Company recognized a provisional amount related to the global intangible low-taxed income (“GILTI”) of the 2017 Tax Act, with no impact to the provision for income tax as the amounts are expected to be offset by the Company’s foreign tax credits. Accordingly, there was no income tax expense (benefit) recorded to the consolidated statement of operations for the three months ended March 31, 2018. The Company expects that the provisions of the Tax Act will be clarified by additional analysis and regulatory guidance, and the clarification could impact its estimated annual effective tax rate. The Company will continue its analysis of these provisional amounts, which are still subject to change during the measurement period, and the Company anticipates further guidance on accounting interpretations from the FASB and application of the law from the Department of the Treasury. With respect to the GILTI provisions specific, the 2017 Tax Act allows companies to make an accounting policy election to either (i) account for GILTI as a component of tax expense in the period in which the entity is subject to the rules or (ii) account for GILTI in the entity’s measurement of deferred taxes. The Company's selection of an accounting policy will depend, in part, on analyzing its global income to determine whether it expects to have future U.S. inclusions in taxable income related to GILTI and, if so, the impact that is expected. Because whether the Company expects to have future U.S. inclusions in taxable income related to GILTI depends on a number of aspects of its estimated future results of global operations, the Company is not yet able to make its accounting policy election. Therefore, the Company has not recorded any deferred tax effects related to GILTI for the three months ended March 31, 2018. The Company recorded a provision for (benefit from) income taxes of $(3.2) million and $7.4 million for the three months ended March 31, 2018 and 2017, respectively. The benefit from income taxes for the three months ended March 31, 2018 is mainly due to projected pretax losses from which the company can benefit from. The income taxes for the three months ended March 31, 2017 was primarily comprised of the Company's U.S. federal, state and foreign taxes and income tax expense recognized from exercises and expiration of out-of-the-money fully vested shares from equity incentive plans. During the three months ended March 31, 2018, the Company paid withholding taxes of $6.1 million. During the three months ended March 31, 2017, the Company paid withholding taxes of $5.5 million. As of March 31, 2018, the Company’s unaudited condensed consolidated balance sheets included net deferred tax assets, before valuation allowance, of approximately $140.5 million, which consists of net operating loss carryovers, tax credit carryovers, amortization, employee stock-based compensation expenses and certain liabilities, partially reduced by deferred tax liabilities associated with deferred revenue and the convertible notes. The Company has U.S. federal deferred tax assets related to research and development credits, foreign tax credits and other tax attributes that can be used to offset federal taxable income in future periods. These credit carryforwards will expire if they are not used within certain time periods. It is possible that some or all of these attributes could ultimately expire unused. If facts and circumstances change in the future, the Company may determine at that time that additional valuation allowance is necessary. Recording additional valuation allowance would materially increase the Company's tax expense in the period applied and would adversely affect its results of operations and statements of financial condition. Changes in the Company's underlying facts or circumstances, such as the impact of the acquisitions, will be continually assessed and the Company will re-evaluate its position accordingly. During the quarter ended March 31, 2018, the Company evaluated the realizability of its newly generated deferred tax assets due to the adoption of ASC 606 based on all available evidence, both positive and negative. The realizability of the Company's net deferred tax assets is dependent on its ability to generate sufficient future taxable income during periods prior to the expiration of tax attributes to fully utilize these assets. The Company determined that it is not more likely than not to realize a portion of the deferred tax asset associated with the foreign tax credits and thus an additional valuation allowance of $15.6 million is recorded in the first quarter of 2018. As of March 31, 2018, the partial valuation allowance on its foreign tax credits totaled $37.1 million. During 2017 the Company determined that it was appropriate to set up a partial valuation allowance on its U.S. federal research and development credits and foreign tax credits of $21.5 million in accordance with FASB ASC 740-10-30-16 to 25. This partial valuation allowance is due to the fact that these credits are not more likely than not to be realized before they expire, as a result of the federal tax rate change from 35% to 21%. As of March 31, 2018, the Company has a total valuation allowance of $66.6 million on U.S. federal, state and foreign deferred tax assets, resulting in net deferred tax assets of $73.9 million. The Company maintains liabilities for uncertain tax positions within its long-term income taxes payable accounts and as a reduction to existing deferred tax assets to the extent tax attributes are available to offset such liabilities. These liabilities involve judgment and estimation and are monitored by management based on the best information available including changes in tax regulations, the outcome of relevant court cases and other information. As of March 31, 2018, the Company had approximately $24.0 million of unrecognized tax benefits, including $21.6 million recorded as a reduction of long-term deferred tax assets and $2.4 million in long-term income taxes payable. If recognized, approximately $2.4 million would be recorded as an income tax benefit. As of December 31, 2017, the Company had $22.6 million of unrecognized tax benefits, including $20.4 million recorded as a reduction of long-term deferred tax assets and $2.2 million recorded in long-term income taxes payable. Although it is possible that some of the unrecognized tax benefits could be settled within the next 12 months, the Company cannot reasonably estimate the outcome at this time. The Company recognizes interest and penalties related to uncertain tax positions as a component of the income tax provision. At March 31, 2018 and December 31, 2017, an immaterial amount of interest and penalties is included in long-term income taxes payable. Rambus files income tax returns for the U.S., California, India, the U.K., the Netherlands and various other state and foreign jurisdictions. The U.S. federal returns are subject to examination from 2014 and forward. The California returns are subject to examination from 2010 and forward. In addition, any research and development credit carryforward or net operating loss carryforward generated in prior years and utilized in these or future years may also be subject to examination. The India returns are subject to examination from fiscal year ending March 2012 and forward. The Company is currently under examination by the IRS for the 2015 tax year, California for the 2010 and 2011 tax years, and New York for the 2013, 2014, and 2015 tax years. The Company’s India subsidiary is under examination by the Indian tax administration for tax years beginning with 2011, except for 2014, which was assessed in the Company's favor. These examinations may result in proposed adjustments to the income taxes as filed during these periods. Management regularly assesses the likelihood of outcomes resulting from income tax examinations to determine the adequacy of their provision for income taxes and believes their provision for unrecognized tax benefits is adequate. Additionally, the Company's future effective tax rates could be adversely affected by earnings being higher than anticipated in countries where the Company has higher statutory rates or lower than anticipated in countries where it has lower statutory rates, by changes in valuation of its deferred tax assets and liabilities or by changes in tax laws or interpretations of those laws.

Income Taxes

On December 22, 2017, the “Tax Cuts & Jobs Act” (hereafter referred to as “U.S. tax reform”) was signed into law and is effective for the Company starting in the quarter ended December 31, 2017. The TCJA provides for numerous significant tax law changes and modifications including the reduction of the U.S. federal corporate income tax rate from 35% to 21%, the requirement for companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously deferred and the creation of new taxes on certain foreign-sourced earnings. The impact on income taxes due to change in legislation is required under the authoritative guidance of Accounting Standards Codification (“ASC”) 740, Income Taxes, to be recognized in the period in which the law is enacted.

In December 2017, the SEC staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (SAB 118), which allows the Company to record provisional amounts for the Tax Act during a measurement period not to extend beyond one year of the enactment date. The Company has recorded significant activity in the period of enactment due to the change in legislation. For the three months ended March 31, 2018, the Company did not have any significant adjustments to its provisional amounts previously recognized. However, in the current period, the Company recognized a provisional amount related to the global intangible low-taxed income (“GILTI”) of the 2017 Tax Act, with no impact to the provision for income tax as the amounts are expected to be offset by the Company’s foreign tax credits. Accordingly, there was no income tax expense (benefit) recorded to the consolidated statement of operations for the three months ended March 31, 2018. The Company expects that the provisions of the Tax Act will be clarified by additional analysis and regulatory guidance, and the clarification could impact its estimated annual effective tax rate. The Company will continue its analysis of these provisional amounts, which are still subject to change during the measurement period, and the Company anticipates further guidance on accounting interpretations from the FASB and application of the law from the Department of the Treasury.

With respect to the GILTI provisions specific, the 2017 Tax Act allows companies to make an accounting policy election to either (i) account for GILTI as a component of tax expense in the period in which the entity is subject to the rules or (ii) account for GILTI in the entity’s measurement of deferred taxes. The Company's selection of an accounting policy will depend, in part, on analyzing its global income to determine whether it expects to have future U.S. inclusions in taxable income related to GILTI and, if so, the impact that is expected. Because whether the Company expects to have future U.S. inclusions in taxable income related to GILTI depends on a number of aspects of its estimated future results of global operations, the Company is not yet able to make its accounting policy election. Therefore, the Company has not recorded any deferred tax effects related to GILTI for the three months ended March 31, 2018.

The Company recorded a provision for (benefit from) income taxes of $(3.2) million and $7.4 million for the three months ended March 31, 2018 and 2017, respectively. The benefit from income taxes for the three months ended March 31, 2018 is mainly due to projected pretax losses from which the company can benefit from. The income taxes for the three months ended March 31, 2017 was primarily comprised of the Company's U.S. federal, state and foreign taxes and income tax expense recognized from exercises and expiration of out-of-the-money fully vested shares from equity incentive plans.

During the three months ended March 31, 2018, the Company paid withholding taxes of $6.1 million. During the three months ended March 31, 2017, the Company paid withholding taxes of $5.5 million.

As of March 31, 2018, the Company’s unaudited condensed consolidated balance sheets included net deferred tax assets, before valuation allowance, of approximately $140.5 million, which consists of net operating loss carryovers, tax credit carryovers, amortization, employee stock-based compensation expenses and certain liabilities, partially reduced by deferred tax liabilities associated with deferred revenue and the convertible notes.

The Company has U.S. federal deferred tax assets related to research and development credits, foreign tax credits and other tax attributes that can be used to offset federal taxable income in future periods. These credit carryforwards will expire if they are not used within certain time periods. It is possible that some or all of these attributes could ultimately expire unused. If facts and circumstances change in the future, the Company may determine at that time that additional valuation allowance is necessary. Recording additional valuation allowance would materially increase the Company's tax expense in the period applied and would adversely affect its results of operations and statements of financial condition. Changes in the Company's underlying facts or circumstances, such as the impact of the acquisitions, will be continually assessed and the Company will re-evaluate its position accordingly.

During the quarter ended March 31, 2018, the Company evaluated the realizability of its newly generated deferred tax assets due to the adoption of ASC 606 based on all available evidence, both positive and negative. The realizability of the Company's net deferred tax assets is dependent on its ability to generate sufficient future taxable income during periods prior to the expiration of tax attributes to fully utilize these assets. The Company determined that it is not more likely than not to realize a portion of the deferred tax asset associated with the foreign tax credits and thus an additional valuation allowance of $15.6 million is recorded in the first quarter of 2018. As of March 31, 2018, the partial valuation allowance on its foreign tax credits totaled $37.1 million.

During 2017 the Company determined that it was appropriate to set up a partial valuation allowance on its U.S. federal research and development credits and foreign tax credits of $21.5 million in accordance with FASB ASC 740-10-30-16 to 25. This partial valuation allowance is due to the fact that these credits are not more likely than not to be realized before they expire, as a result of the federal tax rate change from 35% to 21%.

As of March 31, 2018, the Company has a total valuation allowance of $66.6 million on U.S. federal, state and foreign deferred tax assets, resulting in net deferred tax assets of $73.9 million.

The Company maintains liabilities for uncertain tax positions within its long-term income taxes payable accounts and as a reduction to existing deferred tax assets to the extent tax attributes are available to offset such liabilities. These liabilities involve judgment and estimation and are monitored by management based on the best information available including changes in tax regulations, the outcome of relevant court cases and other information.

As of March 31, 2018, the Company had approximately $24.0 million of unrecognized tax benefits, including $21.6 million recorded as a reduction of long-term deferred tax assets and $2.4 million in long-term income taxes payable. If recognized, approximately $2.4 million would be recorded as an income tax benefit. As of December 31, 2017, the Company had $22.6 million of unrecognized tax benefits, including $20.4 million recorded as a reduction of long-term deferred tax assets and $2.2 million recorded in long-term income taxes payable.

Although it is possible that some of the unrecognized tax benefits could be settled within the next 12 months, the Company cannot reasonably estimate the outcome at this time.

The Company recognizes interest and penalties related to uncertain tax positions as a component of the income tax provision. At March 31, 2018 and December 31, 2017, an immaterial amount of interest and penalties is included in long-term income taxes payable.

Rambus files income tax returns for the U.S., California, India, the U.K., the Netherlands and various other state and foreign jurisdictions. The U.S. federal returns are subject to examination from 2014 and forward. The California returns are subject to examination from 2010 and forward. In addition, any research and development credit carryforward or net operating loss carryforward generated in prior years and utilized in these or future years may also be subject to examination. The India returns are subject to examination from fiscal year ending March 2012 and forward. The Company is currently under examination by the IRS for the 2015 tax year, California for the 2010 and 2011 tax years, and New York for the 2013, 2014, and 2015 tax years. The Company’s India subsidiary is under examination by the Indian tax administration for tax years beginning with 2011, except for 2014, which was assessed in the Company's favor. These examinations may result in proposed adjustments to the income taxes as filed during these periods. Management regularly assesses the likelihood of outcomes resulting from income tax examinations to determine the adequacy of their provision for income taxes and believes their provision for unrecognized tax benefits is adequate.

Additionally, the Company's future effective tax rates could be adversely affected by earnings being higher than anticipated in countries where the Company has higher statutory rates or lower than anticipated in countries where it has lower statutory rates, by changes in valuation of its deferred tax assets and liabilities or by changes in tax laws or interpretations of those laws.