Nature of Operations and Basis of Presentation (Narrative) (Details)		3 Months Ended		6 Months Ended
	Sep. 17, 2017 segment	Jun. 30, 2018 USD ($) state	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment state	Jun. 30, 2017 USD ($)	Jul. 24, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of business segments | segment	2			1
Payment for income taxes				$ 15,037,000	$ 7,628,000
Federal tax refund received				1,503,000	10,000,000
Interest payments				0	0
Decrease in DAC asset related to assumed realization of unrealized gains (losses)		$ 0		0			$ 6,294,000
Federal income tax expense (benefit)		(1,966,000)	$ (4,440,000)	(757,000)	(18,000)
Liability for unrecognized tax benefits		0		0			0
Accumulated other comprehensive income (loss), net of tax		(59,298,000)		(59,298,000)			168,314,000
Retained earnings		$ 824,431,000		$ 824,431,000			608,700,000
Future minimum lease payments due							$ 22,500,000
Future minimum payments due as a percentage of total assets (less than)							1.00%
Property & Casualty Insurance
Segment Reporting Information [Line Items]
Number of states in which we are licensed as insurer | state		46		46
Continuing and Discontinuing Operations
Segment Reporting Information [Line Items]
Federal income tax expense (benefit)				$ 7,350,000	$ 2,250,000
Accounting Standards Update 2016-01
Segment Reporting Information [Line Items]
Accumulated other comprehensive income (loss), net of tax							$ (191,244,000)
Net realized investment gain (loss)		$ 241,000		$ (7,879,000)
Retained earnings							$ 191,200,000
Subsequent Event
Segment Reporting Information [Line Items]
Dividend declared (in dollars per share) | $ / shares						$ 3
Dividend payable						$ 75,000,000