Segment Information Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016		Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Number of Reportable Segments					2
Revenue		$ 662,619	$ 723,760		$ 1,336,245	$ 1,422,195
Acquisition-related (benefit) expense, net		36	850		48	4,314
Income (loss) from operations		(7,398)	(39,753)		(19,078)	(84,901)
Other expense, net		5,878	(11,253)		1,276	(8,635)
Loss from continuing operations before provision for income taxes		(1,520)	(51,006)		(17,802)	(93,536)
Provision for income taxes		3,883	(2,238)		8,470	(1,229)
Net loss from continuing operations		(5,403)	(48,768)		(26,272)	(92,307)
Net loss from discontinued operations		(1,376)	(2,963)		(889)	(5,020)
Net loss		(6,779)	(51,731)		(27,161)	(97,327)
Restructuring Charges		4,584	15,702		7,315	27,215
Share-based Compensation					41,141	66,603
International [Member]
Segment Reporting Information [Line Items]
Revenue	[1]	210,707	206,838		410,976	404,460
Income (loss) from operations	[2],[3]	4,635	(8,469)		7,738	(11,683)
Restructuring Charges					2,400	18,800
Share-based Compensation		1,300	4,900		2,700	7,700
North America [Member]
Segment Reporting Information [Line Items]
Revenue	[1]	451,912	516,922		925,269	1,017,735
Acquisition-related (benefit) expense, net			800			4,300
Income (loss) from operations	[2],[3]	(12,033)	(31,284)	[4]	(26,816)	(73,218)	[4]
Restructuring Charges		2,975	2,806		4,930	8,425
Share-based Compensation		20,000	31,800		38,300	58,900
EMEA [Member]
Segment Reporting Information [Line Items]
Restructuring Charges		1,609	12,896		$ 2,385	$ 18,790
Sales Revenue, Net [Member]
Segment Reporting Information [Line Items]
Concentration of risk, percentage					10.00%	0.00%
United States
Segment Reporting Information [Line Items]
Revenue		$ 442,700	508,800		$ 907,400	$ 1,001,400
Acceleration of Share-Based Compensation [Member] | International [Member]
Segment Reporting Information [Line Items]
Restructuring Charges						2,100
Acceleration of Share-Based Compensation [Member] | North America [Member]
Segment Reporting Information [Line Items]
Restructuring Charges						$ 2,600
Acceleration of Share-Based Compensation [Member] | EMEA [Member]
Segment Reporting Information [Line Items]
Restructuring Charges			$ 2,200

[1] North America includes revenue from the United States of $442.7 million and $508.8 million for the three months ended June 30, 2017 and 2016, respectively, and $907.4 million and $1,001.4 million for the six months ended June 30, 2017 and 2016, respectively. International includes revenue from the United Kingdom of $74.4 million and $78.4 million for the three months ended June 30, 2017 and 2016, respectively, and $139.9 million and $152.4 million for the six months ended June 30, 2017 and 2016, respectively. There were no other individual countries that represented more than 10% of consolidated total revenue for the three and six months ended June 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. 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)Includes stock-based compensation of $20.0 million and $31.8 million for North America and $1.3 million and $4.9 million for International for the three months ended June 30, 2017 and 2016, respectively, and $38.3 million and $58.9 million for North America and $2.7 million and $7.7 million for International for the six months ended June 30, 2017 and 2016, respectively.

[3] Includes restructuring charges of $3.0 million and $2.8 million for North America and $1.6 million and $12.9 million (which includes $2.2 million of stock-based compensation) for International for the three months ended June 30, 2017 and 2016, respectively, and $4.9 million and $8.4 million (which includes $2.6 million of stock-based compensation) for North America and $2.4 million and $18.8 million (which includes $2.1 million of stock-based compensation) for International for the six months ended June 30, 2017 and 2016, respectively.

[4] (2)Includes acquisition-related (benefit) expense, net of $0.8 million and $4.3 million for North America for the three and six months ended June 30, 2016, respectively.