Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets (Details)	12 Months Ended
Dec. 31, 2017
Minimum
Goodwill [Line Items]
Cost allocation period for definite-lived intangible assets	1 year
Maximum
Goodwill [Line Items]
Cost allocation period for definite-lived intangible assets	15 years

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration