Other Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Cash surrender value of corporate-owned life insurance policies	$ 3,949		$ 3,846
Deferred commissions	14,175	$ 12,200	6,803
Restricted Cash	2,477		3,333	$ 3,326
Prepaid expenses, deposits and other	2,795		1,384
Total other long-term assets	23,396	20,689	15,366
Deferred sales commission	20,382
Cash Receipts Held In Escrow
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 1,800		$ 2,700
Accounting Standards Update 2014-09 | Impact of Adoption of Topic 606 on Opening Balance Sheet
Restricted Cash and Cash Equivalents Items [Line Items]
Deferred commissions		5,400
Total other long-term assets		5,323
Deferred sales commission		$ 7,300