Summary of Significant Accounting Policies Income Taxes (Details) $ in Millions	Dec. 31, 2017 USD ($)
ASU 2018-02 Reclassification from AOCI, Tax Effect
Income taxes
Cumulative effect adjustment from adoption of ASU 2018-02	$ 0.6

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

No definition available.

Name:	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant