Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Net premiums earned	$ 738,531	$ 733,281	$ 694,149
Net investment income	95,662	100,012	108,660
Equity in earnings (loss) of unconsolidated subsidiaries	8,033	(5,762)	3,682
Net realized investment gains (losses):
OTTI losses	(13,200)	(10,834)	(19,917)
Portion of OTTI losses recognized in other comprehensive income before taxes	248	1,068	4,572
Net impairment losses recognized in earnings	(12,952)	(9,766)	(15,345)
Other net realized investment gains (losses)	29,361	44,641	(26,294)
Total net realized investment gains (losses)	16,409	34,875	(41,639)
Other income	7,514	7,808	7,227
Total revenues	866,149	870,214	772,079
Expenses
Net losses and loss adjustment expenses	469,158	443,229	410,711
Underwriting, policy acquisition and operating expenses
Operating expense	140,002	139,232	137,508
DPAC Amortization	95,751	88,378	79,556
Segregated portfolio cells dividend expense (income)	15,771	8,142	853
Interest expense	16,844	15,032	14,596
Total expenses	737,526	694,013	643,224
Income before income taxes	128,623	176,201	128,855
Provision for income taxes
Current expense (benefit)	19,666	16,586	28,652
Deferred expense (benefit)	1,693	8,534	(15,994)
Total income tax expense (benefit)	21,359	25,120	12,658
Net income	107,264	151,081	116,197
Other comprehensive income (loss), after tax, net of reclassification adjustments	(2,488)	(6,456)	(34,349)
Comprehensive income	$ 104,776	$ 144,625	$ 81,848
Earnings per share:
Basic (USD per share)	$ 2.01	$ 2.84	$ 2.12
Diluted (USD per share)	$ 2.00	$ 2.83	$ 2.11
Weighted average number of common shares outstanding:
Basic (shares)	53,393	53,216	54,795
Diluted (shares)	53,611	53,448	55,017
Cash dividends declared per common share (USD per share)	$ 5.93	$ 5.93	$ 2.24