Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other assets:
Long-term investments	$ 435,612	$ 425,732
Other	105,184	99,041
Total	540,796	524,773
Accounts payable and accrued liabilities:
Accounts payable	302,101	293,538
Customer deposits	693,004	688,772
Employee related liabilities	260,116	205,901
Other	231,520	190,611
Total	$ 1,486,741	$ 1,378,822