Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets (Details) - Measurement Input, Discount Rate - Goodwill and Indefinite-lived Intangible Assets - Income Approach Valuation Technique	Sep. 30, 2018
Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount rates used for reporting unit valuations	0.10
Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Discount rates used for reporting unit valuations	0.15