Significant Accounting Policies - Contract Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Significant Accounting Policies
Accounts receivable, net	$ 242,757	$ 261,400
Deferred revenues	18,851	16,621
Customer deposits	25,605	27,765
Costs to obtain and fulfill a contract	4,517	4,977
Unbilled receivables, net	24,200	$ 34,100
Revenue recognized from deferred revenue	7,000
Amortization of contract costs	$ 700
Practical expedient on incremental costs of obtaining contracts	true