Goodwill and Intangible Assets - Narrative (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) operating_segment reporting_unit	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 12,876,000				$ 12,876,000				$ 12,876,000	$ 12,876,000
Number of operating segments | operating_segment									1
Number of reporting units | reporting_unit									1
Impairment of goodwill									$ 0
Amortization of acquired intangibles	368,000	$ 369,000	$ 373,000	$ 371,000	366,000	$ 368,000	$ 368,000	$ 368,000	1,481,000	1,470,000	$ 576,000
Capitalized software and development costs	$ 4,000,000				$ 3,000,000				4,000,000	3,000,000
Amortization of capitalized software development costs									$ 500,000
Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life									2 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life									6 years
Cost of revenues
Finite-Lived Intangible Assets [Line Items]
Amortization of acquired intangibles									$ 3,600,000	3,200,000
Operating Expense
Finite-Lived Intangible Assets [Line Items]
Amortization of acquired intangibles									$ 1,500,000	$ 1,500,000
Purchased software and licenses
Finite-Lived Intangible Assets [Line Items]
Estimated useful life									5 years
Purchased software and licenses | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life									5 years