Segment Information Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended			12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016		Dec. 31, 2016
Segment Reporting Information [Line Items]
Number of Reportable Segments				2
Revenue		$ 634,466	$ 686,555	$ 1,970,711	$ 2,108,750
Acquisition-related (benefit) expense, net		0	(9)	48	4,305
Income (loss) from operations		(1,213)	(24,840)	(20,291)	(109,741)
Other expense, net		7,546	(7,917)	8,822	(16,552)
Loss from continuing operations before provision for income taxes		6,333	(32,757)	(11,469)	(126,293)
Provision for income taxes		2,531	1,690	11,001	461
Net loss from continuing operations		3,802	(34,447)	(22,470)	(126,754)
Net loss from discontinued operations		(862)	(1,345)	(1,751)	(6,365)
Net loss		2,940	(35,792)	(24,221)	(133,119)
Restructuring Charges		11,503	1,163	18,818	28,378
Share-based Compensation				60,318	92,360
International [Member]
Segment Reporting Information [Line Items]
Revenue	[1]	220,252	203,274	631,228	607,734
Income (loss) from operations	[2],[3]	5,782	(370)	13,520	(12,053)
Restructuring Charges		4,532	194	6,917	18,984
Share-based Compensation		1,400	700	4,100	5,800
North America [Member]
Segment Reporting Information [Line Items]
Acquisition-related (benefit) expense, net					4,300
Income (loss) from operations	[2],[3]	(6,995)	(24,470)	(33,811)	(97,688)	[4]
Restructuring Charges		6,971	969	11,901	9,394
Share-based Compensation		16,900	24,800	$ 55,200	$ 81,200
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		410,500	$ 476,300	$ 1,317,900	$ 1,477,700
Acceleration of Share-Based Compensation [Member]
Segment Reporting Information [Line Items]
Restructuring Charges				800			$ 4,600
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		$ 800		$ 800	$ 2,600

[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)Includes stock-based compensation of $16.9 million and $24.8 million for North America and $1.4 million and $0.7 million for International for the three months ended September 30, 2017 and 2016, respectively, and $55.2 million and $81.2 million for North America and $4.1 million and $5.8 million for International for the nine months ended September 30, 2017 and 2016, respectively.

[3] Includes restructuring charges of $7.0 million (which includes $0.8 million of stock-based compensation) and $1.0 million for North America and $4.5 million and $0.2 million for International for the three months ended September 30, 2017 and 2016, respectively, and $11.9 million (which includes $0.8 million of stock-based compensation) and $9.4 million (which includes $2.6 million of stock-based compensation) for North America and $6.9 million and $19.0 million (which includes $2.1 million of stock-based compensation) for International for the nine months ended September 30, 2017 and 2016, respectively.

[4] (2)Includes acquisition-related (benefit) expense, net of $4.3 million for North America for the nine months ended September 30, 2016.