Segment and Geographic Area Information - Revenues by principal geographic area (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues by principal geographic area
Revenue	$ 294,312	$ 279,229	$ 293,009	$ 300,056	$ 314,109	$ 305,280	$ 307,722	$ 365,451	$ 1,166,606	$ 1,292,562	$ 1,562,337
U.S.A.
Revenues by principal geographic area
Revenue									941,985	1,057,006	1,286,678
EMEA
Revenues by principal geographic area
Revenue									205,772	213,418	248,466
Other.
Revenues by principal geographic area
Revenue									$ 18,849	$ 22,138	$ 27,193