Income Taxes	6 Months Ended
Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The provision for income taxes for the three months ended June 30, 2018 was an expense of $28.8 million on pretax income of $75.1 million compared to a benefit of $50.5 million on a pretax loss of $142.8 million in the three months ended June 30, 2017. The effective income tax rate was 38.4% for the three months ended June 30, 2018 and 35.4% for the same period in 2017. The quarter-over-quarter change in the effective income tax rate was primarily attributable to tax expense on the gain from divestitures in 2018 partially offset by a reduction in the U.S. tax rate effective for 2018. The provision for income taxes for the six months ended June 30, 2018 was an expense of $5.5 million on pretax income of $32.2 million compared to a benefit of $38.4 million on a pretax loss of $94.3 million in the six months ended June 30, 2017. The effective income tax rate was 17.1% for the six months ended June 30, 2018 and 40.7% for the same period in 2017. The year-over-year change in the effective income tax rate was largely attributable to tax benefits from stock-based compensation during the first half of 2018 that decreased the tax rate on pretax income while such benefits in the first half of 2017 increased the tax rate on pretax losses. In addition to the impact of stock-based compensation, the change in the effective income tax rate was driven by a reduction in the U.S. tax rate effective for 2018 partially offset by tax expense on the gain from divestitures in 2018. The Tax Cuts and Jobs Act (the "Act”) was enacted on December 22, 2017. Among other things, the Act reduced the U.S. federal corporation tax rate from 35% to 21% and requires companies to pay a one-time transition tax on accumulated deferred foreign income (“ADFI”) of foreign subsidiaries that were previously tax deferred. Upon enactment, we remeasured U.S. deferred tax assets and liabilities to reflect the reduced federal corporate tax rate, which reduced our 2017 income tax expense by $123.2 million. We also recorded a provisional amount for the one-time transition tax, which increased our 2017 income tax expense by $63.6 million. During the three months ending June 30, 2018, we recorded an additional $0.7 million provisional expense for the estimated state income tax impact of the one-time transition tax. As of June 30, 2018, we have not completed our accounting for the tax effects of enactment of the Act given the need to obtain, prepare, and analyze various information largely pertinent to the determination of ADFI including, but not limited to, our post-1986 earnings and profits, foreign taxes and amounts held in cash or other specified assets on various measurement dates. As such, the amounts we have recorded are provisional as permitted by the SEC per Staff Accounting Bulletin No. 118 and could change materially. We expect to complete our accounting for the Act by the fourth quarter of 2018 as we complete our analysis and receive additional guidance from the U.S. Government pertaining to the Act. The Act also created a new tax on global intangible low-taxed income ("GILTI") attributable to foreign subsidiaries. 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 accounting policy election with respect to GILTI. We have, however, included an estimate of the current year GILTI tax impact in the 2018 tax provision calculation. The Company had gross unrecognized tax benefits of $60.3 million at both June 30, 2018 and December 31, 2017. It is reasonably possible that gross unrecognized tax benefits will decrease by approximately $5.2 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 appealed the decision and, on July 24, 2018, the appellate court ruled in favor of the Internal Revenue Service. The affected taxpayer has 90 days to petition for review by the Supreme Court. 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 matter. 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 June 30, 2018 was an expense of $28.8 million on pretax income of $75.1 million compared to a benefit of $50.5 million on a pretax loss of $142.8 million in the three months ended June 30, 2017. The effective income tax rate was 38.4% for the three months ended June 30, 2018 and 35.4% for the same period in 2017. The quarter-over-quarter change in the effective income tax rate was primarily attributable to tax expense on the gain from divestitures in 2018 partially offset by a reduction in the U.S. tax rate effective for 2018.

The provision for income taxes for the six months ended June 30, 2018 was an expense of $5.5 million on pretax income of $32.2 million compared to a benefit of $38.4 million on a pretax loss of $94.3 million in the six months ended June 30, 2017. The effective income tax rate was 17.1% for the six months ended June 30, 2018 and 40.7% for the same period in 2017. The year-over-year change in the effective income tax rate was largely attributable to tax benefits from stock-based compensation during the first half of 2018 that decreased the tax rate on pretax income while such benefits in the first half of 2017 increased the tax rate on pretax losses. In addition to the impact of stock-based compensation, the change in the effective income tax rate was driven by a reduction in the U.S. tax rate effective for 2018 partially offset by tax expense on the gain from divestitures in 2018.

The Tax Cuts and Jobs Act (the "Act”) was enacted on December 22, 2017. Among other things, the Act reduced the U.S. federal corporation tax rate from 35% to 21% and requires companies to pay a one-time transition tax on accumulated deferred foreign income (“ADFI”) of foreign subsidiaries that were previously tax deferred. Upon enactment, we remeasured U.S. deferred tax assets and liabilities to reflect the reduced federal corporate tax rate, which reduced our 2017 income tax expense by $123.2 million. We also recorded a provisional amount for the one-time transition tax, which increased our 2017 income tax expense by $63.6 million.

During the three months ending June 30, 2018, we recorded an additional $0.7 million provisional expense for the estimated state income tax impact of the one-time transition tax. As of June 30, 2018, we have not completed our accounting for the tax effects of enactment of the Act given the need to obtain, prepare, and analyze various information largely pertinent to the determination of ADFI including, but not limited to, our post-1986 earnings and profits, foreign taxes and amounts held in cash or other specified assets on various measurement dates. As such, the amounts we have recorded are provisional as permitted by the SEC per Staff Accounting Bulletin No. 118 and could change materially. We expect to complete our accounting for the Act by the fourth quarter of 2018 as we complete our analysis and receive additional guidance from the U.S. Government pertaining to the Act.

The Act also created a new tax on global intangible low-taxed income ("GILTI") attributable to foreign subsidiaries. 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 accounting policy election with respect to GILTI. We have, however, included an estimate of the current year GILTI tax impact in the 2018 tax provision calculation.

The Company had gross unrecognized tax benefits of $60.3 million at both June 30, 2018 and December 31, 2017. It is reasonably possible that gross unrecognized tax benefits will decrease by approximately $5.2 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 appealed the decision and, on July 24, 2018, the appellate court ruled in favor of the Internal Revenue Service. The affected taxpayer has 90 days to petition for review by the Supreme Court. 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 matter. The Company will monitor developments related to this case and the potential impact of those developments on the Company’s consolidated financial statements.