Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) reporting_unit segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Accounting Policies [Abstract]
Number of reportable segments | segment	5
Insurance policy duration (years)	1 year
Recorded allowances for credit losses	$ 1,600,000	$ 1,300,000
Estimated credit losses and actual write-offs, net of recoveries	300,000
Earned but unbilled premiums	$ 4,300,000	4,300,000
Minimum period for claims resolution (years)	5 years
Leases classified as financing leases	$ 0
Number of of reporting units (in reporting units) | reporting_unit	5
Number of reporting units with goodwill (in reporting units) | reporting_unit	3
Goodwill impairment loss	$ 0	0	$ 0
Building and Building Improvements
Property, Plant and Equipment [Line Items]
Real estate accumulated depreciation	25,700,000	25,200,000
Depreciation	$ 1,000,000.0	$ 1,200,000	$ 1,100,000