Organizational Restructuring (Narrative) (Details) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	[1]	Dec. 31, 2019 USD ($)		Dec. 31, 2018 USD ($) lease
Restructuring Cost and Reserve [Line Items]
Restructuring charges (reversal)	$ (1,886)	$ 2,270	$ 2,949	$ (70)	$ 0		$ 3,263	[1]	$ 11,837	[1]
2018 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Percentage of positions eliminated									10.00%
Number of operating leases terminated | lease									1
Number of sub-leases extended | lease									3
Restructuring cost incurred									$ 8,100
Restructuring charges (reversal)							$ (2,195)		$ 10,263
May 2019 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Percentage of positions eliminated							10.00%
Restructuring charges (reversal)							$ 3,100
August 2019 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Percentage of positions eliminated							8.00%
Restructuring charges (reversal)							$ 2,500

[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