Other Non-Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Other Assets, Noncurrent [Abstract]
Deferred sales incentive compensation	$ 7,014		$ 0
Assets to fund deferred compensation liability	6,346		5,185
Lease and other deposits	4,341		4,906
Investments in private companies	2,862		2,731
Unamortized issuance costs on revolving credit facility	2,251		3,106
Other	2,484		1,248
Total other non-current assets	$ 25,298	$ 22,491	$ 17,176