Summary of Significant Accounting Policies - Property and equipment (Details)	12 Months Ended
Dec. 31, 2018
Facilities \| Minimum
Property and equipment
Estimated useful lives	10 years
Facilities \| Maximum
Property and equipment
Estimated useful lives	40 years
Furniture, fixtures and equipment \| Minimum
Property and equipment
Estimated useful lives	3 years
Furniture, fixtures and equipment \| Maximum
Property and equipment
Estimated useful lives	10 years

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

No definition available.

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