Basis of Presentation and Summary of Significant Accounting Policies - Contract Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Basis of Presentation and Summary of Significant Accounting Policies
Accounts receivable, net	$ 261,400	$ 270,812	$ 260,438	$ 266,660	$ 278,064	$ 253,986	$ 262,260	$ 238,680
Deferred revenues	16,621	16,940
Customer deposits	27,765	34,235	$ 30,161	$ 28,914	$ 28,410	$ 39,419	$ 36,997	$ 36,542
Costs to obtain and fulfill a contract	4,977	6,623
Unbilled receivables, net	34,135	39,498
Revenue recognized from deferred revenue	14,400
Amortization of contract costs	$ 2,900	$ 3,100
Practical expedient on incremental costs of obtaining contracts	true