Basis of Presentation and Summary of Significant Accounting Policies - Contract Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Basis of Presentation and Summary of Significant Accounting Policies
Accounts receivable, net	$ 270,812	$ 229,704
Deferred revenues	16,940	13,717
Costs to obtain and fulfill a contract	18,624	22,929
Customer deposits	34,235	31,656
Unbilled receivables, net	39,498	$ 28,449
Revenue recognized from deferred revenue	13,400
Amortization of contract costs	$ 10,500
Practical expedient on incremental costs of obtaining contracts	true