Revenue Information and Deferred Sales Commissions - Narrative (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 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	3,100,000	3,100,000
Amortization of capitalized contract costs	400,000	800,000
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	$ 600,000	$ 1,000,000