Segment and Geographic Area Information - Revenues by principal geographic area (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues by principal geographic area
Revenue	$ 393,586	$ 373,545	$ 390,849	$ 404,357	$ 399,643	$ 383,030	$ 410,382	$ 393,167	$ 795,206	$ 803,549	$ 1,168,751	$ 1,186,579	$ 1,562,337	$ 1,586,222	$ 1,145,891
United States
Revenues by principal geographic area
Revenue													1,286,678	1,347,516	1,000,827
EMEA
Revenues by principal geographic area
Revenue													248,466	211,314	130,098
Other
Revenues by principal geographic area
Revenue													$ 27,193	$ 27,392	$ 14,966