Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Earned premiums (affiliated net assumed $458.0, $472.0 and $437.6, respectively)	$ 1,238,000	$ 1,276,100	$ 1,291,100
Net investment income (affiliates $4.9, $4.9 and $4.9, respectively)	84,900	78,800	74,700
Net realized gain on investments:
Total other-than-temporary impairment losses	0	(3,500)	(6,800)
Other net realized investment gains	(49,700)	68,600	43,300
Total net realized gain on investments	(49,700)	65,100	36,500
Other income (affiliates $2.3, $2.3 and $2.1, respectively)	2,600	2,300	2,300
Total revenues	1,275,800	1,422,300	1,404,600
Losses and loss expenses (affiliated net assumed $379.6, $383.8 and $293.3, respectively)	796,400	918,300	942,300
Acquisition and operating expenses (affiliated net assumed $270.7, $285.8 and $248.6, respectively)	449,800	455,200	430,100
Interest expense (affiliates $0.8, $0.8 and $0.7, respectively)	5,700	5,900	5,500
Other expenses	11,000	7,900	7,900
Total expenses	1,262,900	1,387,300	1,385,800
Income before federal income taxes	12,900	35,000	18,800
Current	(1,100)	400	(1,700)
Deferred Income Tax Expense (Benefit)	1,200	52,400	1,300
Total federal income tax expense (benefit)	100	52,800	(400)
Net (loss) income	$ 12,800	$ (17,800)	$ 19,200
(Loss) earnings per common share:
Basic (usd per share)	$ 0.30	$ (0.42)	$ 0.46
Diluted (usd per share)	0.29	(0.42)	0.46
Dividends paid per common share (usd per share)	$ 0.40	$ 0.40	$ 0.40