Income Taxes	3 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The provision for income taxes for the three months ended March 31, 2018 was a benefit of $(23.3) million on a pretax loss of $(42.9) million compared to an expense of $12.1 million on pretax income of $48.5 million in the three months ended March 31, 2017. The effective income tax rate was 54.3% for the three months ended March 31, 2018 and 24.9% for the same period in 2017. The quarter-over-quarter change in the effective income tax rate was primarily attributable to the relative impact of stock-based compensation benefits quarter-over-quarter. The tax benefits from stock-based compensation during the first quarter of 2018 increased the tax rate on pretax losses while such benefits in the first quarter of 2017 decreased the tax rate on pretax income. In addition to the impact of stock-based compensation, the change in the effective income tax rate quarter-over-quarter was driven by a reduction in the U.S. tax rate effective for 2018 as well as tax benefits recognized in 2018 for unrealized capital losses on the divestiture of the CEB Talent Assessment business. The Tax Cuts and Jobs Act (the "Act”) was enacted on December 22, 2017. Among other things, the Act reduces the U.S. federal corporation tax rate from 35% to 21%, requires companies to pay a one-time transition tax on accumulated deferred foreign income (“ADFI”) of foreign subsidiaries that were previously tax deferred and creates a new tax on global intangible low-taxed income (“GILTI”) attributable to foreign subsidiaries. As of March 31, 2018, we have not completed our accounting for the tax effects of enactment of the Act because all of the necessary information is not currently available, prepared or analyzed. As such, the amounts we have recorded are provisional estimates and as permitted by the SEC per Staff Accounting Bulletin No. 118. We expect to complete the accounting for the impact of tax reform by the fourth quarter of 2018 as we complete our analysis and receive additional guidance from the Internal Revenue Service pertaining to the Act. Companies have the option to account for the GILTI tax as a period cost in the period incurred, or to recognize deferred taxes for temporary differences including outside basis differences expected to reverse as a result of the GILTI provisions. The Company has not yet determined its policy election with respect to GILTI. We have, however, included an estimate of the current year GILTI impact in the 2018 tax provision calculation. Upon enactment of the Act, we remeasured U.S. deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, which is generally 21% and recorded a provisional amount which reduced our 2017 income tax expense by $123.2 million. We are still analyzing certain aspects of the Act and refining our deferred tax calculations, which could affect the measurement of these balances or give rise to new deferred tax amounts. We did not adjust the initial provisional amount in the three months ended March 31, 2018. The tax on ADFI is based on post-1986 earnings and profits ("E&P") of our foreign subsidiaries that were previously deferred from U.S. income taxes. We recorded a provisional amount for this one-time transition tax liability, resulting in an increase in income tax expense of $63.6 million in 2017. We have not yet completed our calculation of the tax on ADFI given the need to obtain, prepare and analyze various information relevant to such calculation including, but not limited to, our post-1986 E&P, foreign taxes and amounts held in cash or other specified assets on various measurement dates. We did not adjust the initial provisional amount in the three months ended March 31, 2018. As of March 31, 2018 and December 31, 2017, the Company had gross unrecognized tax benefits of $63.2 million and $60.3 million, respectively. It is reasonably possible that gross unrecognized tax benefits will decrease by approximately $8.0 million within the next 12 months, due to the anticipated closure of audits and the expiration of certain statutes of limitation. In July 2015, the United States Tax Court (the “Court”) issued an opinion relating to the treatment of stock-based compensation expense in an inter-company cost-sharing arrangement. In its opinion, the Court held that affiliated companies may exclude stock-based compensation expense from their cost-sharing arrangement. The Internal Revenue Service is appealing the decision. Because of uncertainty related to the final resolution of this litigation and the recognition of potential benefits to the Company, the Company has not recorded any financial statement benefit associated with this decision. The Company will monitor developments related to this case and the potential impact of those developments on the Company’s consolidated financial statements.

Income Taxes

The provision for income taxes for the three months ended March 31, 2018 was a benefit of $(23.3) million on a pretax loss of $(42.9) million compared to an expense of $12.1 million on pretax income of $48.5 million in the three months ended March 31, 2017. The effective income tax rate was 54.3% for the three months ended March 31, 2018 and 24.9% for the same period in 2017.

The quarter-over-quarter change in the effective income tax rate was primarily attributable to the relative impact of stock-based compensation benefits quarter-over-quarter. The tax benefits from stock-based compensation during the first quarter of 2018 increased the tax rate on pretax losses while such benefits in the first quarter of 2017 decreased the tax rate on pretax income. In addition to the impact of stock-based compensation, the change in the effective income tax rate quarter-over-quarter was driven by a reduction in the U.S. tax rate effective for 2018 as well as tax benefits recognized in 2018 for unrealized capital losses on the divestiture of the CEB Talent Assessment business.

The Tax Cuts and Jobs Act (the "Act”) was enacted on December 22, 2017. Among other things, the Act reduces the U.S. federal corporation tax rate from 35% to 21%, requires companies to pay a one-time transition tax on accumulated deferred foreign income (“ADFI”) of foreign subsidiaries that were previously tax deferred and creates a new tax on global intangible low-taxed income (“GILTI”) attributable to foreign subsidiaries. As of March 31, 2018, we have not completed our accounting for the tax effects of enactment of the Act because all of the necessary information is not currently available, prepared or analyzed. As such, the amounts we have recorded are provisional estimates and as permitted by the SEC per Staff Accounting Bulletin No. 118. We expect to complete the accounting for the impact of tax reform by the fourth quarter of 2018 as we complete our analysis and receive additional guidance from the Internal Revenue Service pertaining to the Act.

Companies have the option to account for the GILTI tax as a period cost in the period incurred, or to recognize deferred taxes for temporary differences including outside basis differences expected to reverse as a result of the GILTI provisions. The Company has not yet determined its policy election with respect to GILTI. We have, however, included an estimate of the current year GILTI impact in the 2018 tax provision calculation.

Upon enactment of the Act, we remeasured U.S. deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, which is generally 21% and recorded a provisional amount which reduced our 2017 income tax expense by $123.2 million. We are still analyzing certain aspects of the Act and refining our deferred tax calculations, which could affect the measurement of these balances or give rise to new deferred tax amounts. We did not adjust the initial provisional amount in the three months ended March 31, 2018.

The tax on ADFI is based on post-1986 earnings and profits ("E&P") of our foreign subsidiaries that were previously deferred from U.S. income taxes. We recorded a provisional amount for this one-time transition tax liability, resulting in an increase in income tax expense of $63.6 million in 2017. We have not yet completed our calculation of the tax on ADFI given the need to obtain, prepare and analyze various information relevant to such calculation including, but not limited to, our post-1986 E&P, foreign taxes and amounts held in cash or other specified assets on various measurement dates. We did not adjust the initial provisional amount in the three months ended March 31, 2018.

As of March 31, 2018 and December 31, 2017, the Company had gross unrecognized tax benefits of $63.2 million and $60.3 million, respectively. It is reasonably possible that gross unrecognized tax benefits will decrease by approximately $8.0 million within the next 12 months, due to the anticipated closure of audits and the expiration of certain statutes of limitation.

In July 2015, the United States Tax Court (the “Court”) issued an opinion relating to the treatment of stock-based compensation expense in an inter-company cost-sharing arrangement. In its opinion, the Court held that affiliated companies may exclude stock-based compensation expense from their cost-sharing arrangement. The Internal Revenue Service is appealing the decision. Because of uncertainty related to the final resolution of this litigation and the recognition of potential benefits to the Company, the Company has not recorded any financial statement benefit associated with this decision. The Company will monitor developments related to this case and the potential impact of those developments on the Company’s consolidated financial statements.