Significant Event (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Extraordinary And Unusual Items Abstract
Special provision due to significant event	$ 32.4
Incurred costs due to hurricane	2.2
Insurance reimbursement	1.0
Other assets receivable from insurance	1.2
Estimated total losses	$ 6.6