Restructuring Restructuring Costs (Details) $ in Thousands		3 Months Ended				9 Months Ended				12 Months Ended
		Sep. 30, 2017 USD ($) employee		Sep. 30, 2016 USD ($) employee		Sep. 30, 2017 USD ($) employee		Sep. 30, 2016 USD ($) employee		Dec. 31, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Revenue		$ 634,466		$ 686,555		$ 1,970,711		$ 2,108,750
Restructuring Charges		$ 11,503		$ 1,163		$ 18,818		$ 28,378
Restructuring and Related Cost, Number of Positions Eliminated | employee		400		150		750		700
North America [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges		$ 6,971		$ 969		$ 11,901		$ 9,394
International [Member]
Restructuring Cost and Reserve [Line Items]
Revenue	[1]	220,252		203,274		631,228		607,734
Restructuring Charges		4,532		194		6,917		18,984
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Costs						80,200
Restructuring Charges		7,958	[2]	178	[3]	13,032	[4]	24,556	[5]
Employee Severance [Member] | North America [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges		3,662		274		8,127		6,487
Employee Severance [Member] | International [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges		4,296		(96)		4,905		18,069
Asset Impairments Related to Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Costs						7,500
Restructuring Charges		0		0		0		45
Asset Impairments Related to Restructuring [Member] | North America [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges		0		0		0		45
Asset Impairments Related to Restructuring [Member] | International [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges		0		0		0		0
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges		3,545		985		5,786		3,777
Other Restructuring [Member] | North America [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges		3,309		695		3,774		2,862
Other Restructuring [Member] | International [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges		236		$ 290		2,012		915
Acceleration of Share-Based Compensation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges						800				$ 4,600
Acceleration of Share-Based Compensation [Member] | North America [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges		$ 800				$ 800		2,600
Acceleration of Share-Based Compensation [Member] | International [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges								$ 2,100
Facility Closing [Member] | ROW [Member]
Restructuring Cost and Reserve [Line Items]
Number of Countries in which Entity Operates		17				17

[1] North America includes revenue from the United States of $410.5 million and $476.3 million for the three months ended September 30, 2017 and 2016, respectively, and $1,317.9 million and $1,477.7 million for the nine months ended September 30, 2017 and 2016, respectively. International includes revenue from the United Kingdom of $82.2 million and $73.5 million for the three months ended September 30, 2017 and 2016, respectively, and $222.1 million and $225.9 million for the nine months ended September 30, 2017 and 2016, respectively. There were no other individual countries that represented more than 10% of consolidated total revenue for the three and nine months ended September 30, 2017 and 2016. In prior periods, revenue was attributed to individual countries based on the domicile of the legal entities within the Company's consolidated group that undertook those transactions. Beginning in the second quarter of 2017, the Company updated its attribution of revenue by country in the current period to be based on the location of the customer. Prior period revenue amounts by country have been retrospectively adjusted to reflect that change in attribution.

[2] (1)The employee severance and benefit costs for the three months ended September 30, 2017 relates to the termination of approximately 400 employees. Substantially all of the remaining cash payments for those costs are expected to be disbursed through April 30, 2018.

[3] The employee severance and benefit costs for the three months ended September 30, 2016 related to the termination of approximately 150 employees.

[4] The employee severance and benefit costs for the nine months ended September 30, 2017 relates to the termination of approximately 750 employees. Substantially all of the remaining cash payments for those costs are expected to be disbursed through April 30, 2018.

[5] (1)The employee severance and benefit costs for the nine months ended September 30, 2016 related to the termination of approximately 700 employees.