Segment Information - Revenues By Region (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers [Line Items]
Total revenues	$ 587,044,000	$ 595,962,000	$ 585,890,000	$ 607,221,000	$ 550,776,000	$ 486,747,000	$ 503,082,000	$ 477,592,000	$ 2,376,117,000	$ 2,018,197,000	$ 2,013,186,000
United States and Canada [Member]
Revenues from External Customers [Line Items]
Total revenues									1,442,792,000	1,137,508,000	1,126,787,000
EMEA [Member]
Revenues from External Customers [Line Items]
Total revenues									733,732,000	672,942,000	698,106,000
Other Countries [Member]
Revenues from External Customers [Line Items]
Total revenues									$ 199,593,000	$ 207,747,000	$ 188,293,000