Revenue Information and Deferred Sales Commissions - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract asset balance	$ 4,100,000	$ 4,100,000	$ 3,300,000
Sales commission
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred sales commission	3,200,000	3,200,000
Amortization of capitalized contract costs	500,000	1,200,000
Impairment loss	0	0
Sales commission | Balances Without Adoption of New Revenue Standard | ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales commissions expense	$ 500,000	$ 1,500,000