Revenue Recognition (ASC 606 Adoption) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 71,594	$ 64,583	$ 199,971	$ 176,043
Income tax expense (benefit)	67	85	112	(2,459)
Net income	$ 5,711	$ 5,034	$ 13,317	$ 9,596
Basic earnings per share (in dollars per share)	$ 0.22	$ 0.20	$ 0.51	$ 0.39
Diluted earnings per share (in dollars per share)	$ 0.21	$ 0.19	$ 0.48	$ 0.36
Other assets	$ 1,330		$ 1,330		$ 1,618
Current portion of deferred revenue	5,121		5,121		4,538
Other long-term liabilities	4,500		4,500		3,942
Stockholders' equity	$ 180,692		$ 180,692		169,528
Accounting Standards Update 2014-09 | As previously reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue		$ 64,742		$ 176,386
Income tax expense (benefit)		93		(2,441)
Net income		$ 5,185		$ 9,921
Basic earnings per share (in dollars per share)		$ 0.21		$ 0.40
Diluted earnings per share (in dollars per share)		$ 0.19		$ 0.38
Other assets					1,576
Current portion of deferred revenue					2,311
Other long-term liabilities					882
Stockholders' equity					174,773
Accounting Standards Update 2014-09 | ASC 606 adjustment
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue		$ (159)		$ (343)
Income tax expense (benefit)		(8)		(18)
Net income		$ (151)		$ (325)
Basic earnings per share (in dollars per share)		$ (0.01)		$ (0.01)
Diluted earnings per share (in dollars per share)				$ (0.02)
Other assets					42
Current portion of deferred revenue					2,227
Other long-term liabilities					3,060
Stockholders' equity					$ (5,245)