Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Taxes [Line Items]
Effective income tax rate	27.10%	26.70%
Income before income taxes, domestic operations	$ (8,700)	$ 100
Income before income taxes, foreign operations	34,600	35,100
Tax Cuts and Jobs Act, Incomplete Accounting, Change in Tax Rate, Deferred Tax Liability, Provisional Income Tax Benefit			$ 33,300
Tax Cuts and Jobs Act, Incomplete Accounting, Provisional Income Tax Expense (Benefit)			49,200
Liabilities for uncertain income tax positions	53,300		52,200
Cash paid for income taxes	5,400	$ 6,500
Prepaid tax payments	$ 3,000		$ 6,000
California Franchise Tax Board [Member]
Income Taxes [Line Items]
Income Tax Examination, Year under Examination							2013	2012
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Income Tax Examination, Year under Examination						2014	2013	2012
Massachusetts Department of revenue [Member]
Income Taxes [Line Items]
Income Tax Examination, Year under Examination					2015	2014
New York State Division of Taxation and Finance [Member]
Income Taxes [Line Items]
Income Tax Examination, Year under Examination						2014	2013	2012	2011
Georgia Department of Revenue [Member]
Income Taxes [Line Items]
Income Tax Examination, Year under Examination				2016	2015	2014
Ministry of the Economy, Finance and Industry, France [Member]
Income Taxes [Line Items]
Income Tax Examination, Year under Examination				2016	2015	2014	2013	2012	2011