Description of business - (Details)	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of states in which company is authorized to write business	50

The number of states the entity operates in as of the balance sheet date.

No definition available.

Name:	us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant