Investments (Narrative) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) Business Issuer investment_interest Security	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Business Issuer investment_interest Security	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) Issuer Security
Reclassifications from AOCI to net income:
Number of Investment Affiliates Exceeding Shareholder's Equity Ten Percent Threshold Limit | investment_interest	0		0
Threshold Limit Of Investments Based On Shareholders Equity	10.00%		10.00%
Securities on deposit with state insurance departments	$ 45,700		$ 45,700
Business owned life insurance cost	$ 33,000		$ 33,000
Number of LPs / LLCs with investment ownership percent over 25% | Business	3		3
Investment in unconsolidated subsidiaries	$ 390,214		$ 390,214		$ 330,591
OTTI losses	(404)	$ 0	(404)	$ (419)
Net impairment losses recognized in earnings	404	0	404	171
Portion of noncredit OTTI losses recognized in OCI	$ 0	$ 0	$ 0	248
Tax Credit Partnerships Almost 100% Ownership
Reclassifications from AOCI to net income:
Number of tax credit partnerships almost 100% ownership percentage | investment_interest	2		2
Investment in unconsolidated subsidiaries	$ 28,500		$ 28,500		32,500
Tax Credit Partnerships Less Than 20% Ownership
Reclassifications from AOCI to net income:
Investment in unconsolidated subsidiaries	46,400		46,400		52,100
Other Limited Partnerships and Limited Liability Company, Greater Than 25% Ownership
Reclassifications from AOCI to net income:
Investment in unconsolidated subsidiaries	28,400		28,400		30,800
Other Limited Partnerships and Limited Liability Company Less than 25% Ownership
Reclassifications from AOCI to net income:
Investment in unconsolidated subsidiaries	$ 281,900		$ 281,900		$ 209,100
Maximum | Tax Credit Partnerships Almost 100% Ownership
Reclassifications from AOCI to net income:
Investment ownership percentage	100.00%		100.00%
Maximum | Tax Credit Partnerships Less Than 20% Ownership
Reclassifications from AOCI to net income:
Investment ownership percentage	20.00%		20.00%
Fixed maturities
Reclassifications from AOCI to net income:
Required FAL Deposit	$ 123,600		$ 123,600
Short-term investments
Reclassifications from AOCI to net income:
Required FAL Deposit	$ 1,000		$ 1,000
Non Government-Backed
Reclassifications from AOCI to net income:
Number of debt securities in unrealized loss position | Security	1,024		1,024		629
Debt securities in unrealized loss position as percentage of total debt securities held	50.00%		50.00%		26.50%
Number of issuers in unrealized loss position | Issuer	548		548		375
Single greatest unrealized loss position	$ 600		$ 600		$ 400
Second greatest unrealized loss position	$ 400		$ 400		$ 300
Corporate Bond Securities
Reclassifications from AOCI to net income:
Portion of noncredit OTTI losses recognized in OCI				$ 200