Organizational Restructuring Accrued Restructuring Expenses, Changes in Accrued Amounts and Additional Restructuring Costs (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Restructuring Reserve [Roll Forward]
Restructuring expense	$ (1,886)	$ 2,270	$ 2,949	$ (70)	$ 0	[1]	$ 3,263	[1]	$ 11,837	[1]
2018 Restructuring Plan
Restructuring Reserve [Roll Forward]
Accrued Beginning Balance				7,011	0		7,011
Adoption of ASC 842							(2,518)
Restructuring expense							(2,195)		10,263
Payments							(2,298)		(3,250)
Foreign exchange									(2)
Accrued Ending Balance	0						0		7,011
Write-off of certain lease-related liabilities									(700)
Stock-based compensation									500
Accelerated depreciation									500
Other expenses									100
2018 Restructuring Plan | Severance pay and benefits
Restructuring Reserve [Roll Forward]
Accrued Beginning Balance				4,493	0		4,493
Adoption of ASC 842							0
Restructuring expense							(2,195)		7,145
Payments							(2,298)		(2,652)
Foreign exchange									0
Accrued Ending Balance	0						0		4,493
2018 Restructuring Plan | Short-term lease exit and other direct costs
Restructuring Reserve [Roll Forward]
Accrued Beginning Balance				708	0		708
Adoption of ASC 842							(708)
Restructuring expense							0		1,271
Payments							0		(561)
Foreign exchange									(2)
Accrued Ending Balance	0						0		708
2018 Restructuring Plan | Long-term lease exit and other direct costs
Restructuring Reserve [Roll Forward]
Accrued Beginning Balance				$ 1,810	0		1,810
Adoption of ASC 842							(1,810)
Restructuring expense							0		1,847
Payments							0		(37)
Foreign exchange									0
Accrued Ending Balance	0						0		$ 1,810
May 2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Accrued Beginning Balance					294
Restructuring expense							3,100
Payments					(294)		(2,847)
Accrued Ending Balance	294				0		294
May 2019 Restructuring Plan | Severance pay and benefits
Restructuring Reserve [Roll Forward]
Restructuring expense							3,141
August 2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Accrued Beginning Balance					698
Restructuring expense							2,500
Payments					(698)		(1,756)
Accrued Ending Balance	$ 698				$ 0		698
August 2019 Restructuring Plan | Severance pay and benefits
Restructuring Reserve [Roll Forward]
Restructuring expense							$ 2,454

[1] Stock-based compensation expense is included in the line items above as follows: Years Ended December 31,202020192018Cost of revenues$1,288 $1,852 $6,349 Selling and marketing2,226 3,615 9,452 Research and development886 1,981 6,580 General and administrative5,673 9,247 14,770 Restructuring— (137)468 Total stock-based compensation expense$10,073 $16,558 $37,619