Related Party Transactions (Transaction with Related Parties) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Prepaid expenses and other current assets	$ 16,910	$ 15,357
Accrued expenses	48,380	55,507
Senior secured convertible notes	192,895	184,075
Financing derivatives	11,300	21,587
Other non-current liabilities	19,600	13,284
Investor
Related Party Transaction [Line Items]
Revenues	13,314	17,464	$ 12,662
Interest income	(24,480)	(23,494)	(16,023)
Accounts receivable, net	4,045	2,698
Prepaid expenses and other current assets	1,496	1,180
Accounts payable	2,817	2,510
Accrued expenses	835	6,902
Other non-current liabilities	6,120	0
WPP | Investor
Related Party Transaction [Line Items]
Revenues	13,315	15,858	11,610
Interest income	0	0	343
Accounts receivable, net	4,045	2,542
Prepaid expenses and other current assets	1,496	1,180
Accounts payable	2,817	2,510
Accrued expenses	835	716
Contract liabilities	3,538	1,361
WPP | Investor | Cost of revenues
Related Party Transaction [Line Items]
Expenses	10,094	10,455	11,077
WPP | Investor | General and administrative
Related Party Transaction [Line Items]
Expenses	316	539	99
Starboard Value LP | Investor
Related Party Transaction [Line Items]
Interest income	(33,300)	(30,800)	$ (16,400)
Accrued expenses	0	6,120
Senior secured convertible notes	192,895	184,075
Financing derivatives	11,300	21,587
Other non-current liabilities	$ 6,120	$ 0