Revenue Recognition (Revenue by Geographic Region) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue		$ 64,213	$ 56,493	$ 184,114	$ 161,486
United States
Disaggregation of Revenue [Line Items]
Revenue		37,033	35,519	106,676	101,282
Other Americas
Disaggregation of Revenue [Line Items]
Revenue	[1]	2,402	1,744	6,208	5,684
Total Americas
Disaggregation of Revenue [Line Items]
Revenue		39,435	37,263	112,884	106,966
EMEA
Disaggregation of Revenue [Line Items]
Revenue	[2],[3]	18,536	14,175	52,974	41,640
APAC
Disaggregation of Revenue [Line Items]
Revenue	[4]	6,242	5,055	18,256	12,880
United Kingdom
Disaggregation of Revenue [Line Items]
Revenue		$ 11,100	$ 10,200	$ 34,700	$ 28,400

[1] Canada, Latin America and South America

[2] Europe, the Middle East and Africa (“EMEA”)

[3] Includes revenues from the United Kingdom of $11.1 million and $10.2 million for the three months ended September 30, 2018 and 2017, respectively, and $34.7 million and $28.4 million nine months ended September 30, 2018 and 2017, respectively.

[4] Asia-Pacific (“APAC”)