Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Accounting Policies [Abstract]
Number of reportable segments | segment	4
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Insurance policy duration (years)	1 year
Recorded allowances for credit losses (less than)	$ 1,500,000	$ 1,500,000
Estimated credit losses (more than)	700,000	700,000
Earned but unbilled premiums	$ 4,300,000	3,900,000
Minimum period for claims resolution (years)	5 years
Property, Plant and Equipment [Line Items]
Reversal of tax position due to favorable resolution of IRS exam	$ 0	0	$ 4,823,000
Real estate depreciation expense	6,452,000	7,437,000	6,956,000
Estimated aggregate amortization of intangible assets for 2017	5,600,000
Estimated aggregate amortization of intangible assets for 2018	5,600,000
Estimated aggregate amortization of intangible assets for 2019	5,600,000
Estimated aggregate amortization of intangible assets for 2020	5,600,000
Estimated aggregate amortization of intangible assets for 2021	$ 5,600,000
Number of reporting units | segment	2
Goodwill impairment loss	$ 0	0
Building and Building Improvements
Property, Plant and Equipment [Line Items]
Real estate accumulated depreciation	22,900,000	24,200,000
Real estate depreciation expense	$ 1,400,000	1,500,000	$ 1,500,000
Parent Company | Accounting Standards Update 2015-03 | Other Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt issuance costs		$ 2,100,000