Segment Information - Financial Information by Major Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Total revenue	$ 277,285	$ 339,099	$ 364,774	$ 325,807	$ 256,396	$ 382,465	$ 324,747	$ 241,362	$ 1,306,965	$ 1,204,970	$ 1,089,048
Long-lived assets:
Total long-lived assets	353,083				324,155				353,083	324,155	226,870
United States
Revenue:
Total revenue									913,210	855,304	726,436
Long-lived assets:
Total long-lived assets	180,345				182,611				180,345	182,611	139,479
EMEA
Revenue:
Total revenue									209,824	205,028	220,046
Long-lived assets:
Total long-lived assets	43,630				37,083				43,630	37,083	15,714
Canada
Revenue:
Total revenue									183,931	144,638	142,566
Long-lived assets:
Total long-lived assets	$ 129,108				$ 104,461				$ 129,108	$ 104,461	$ 71,677