Revenue from Contracts with Customers - Unsatisfied Performance Obligations Period (Details)	Sep. 30, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations
Subscription services | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations	3 months
Subscription services | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations	1 year
Subscription services | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations	1 year
Subscription services | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations
Other business services | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations	3 months
Other business services | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations	1 year
Other business services | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations	1 year
Other business services | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Unsatisfied Performance Obligations
Expected period to recognize revenue of remaining performance obligations