Condensed Consolidated Statements of Earnings and Comprehensive Earnings - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Consolidated Statements of Earnings and Comprehensive Earnings
Net premiums earned	$ 839,111,000	$ 791,366,000	$ 737,937,000
Net investment income	68,870,000	62,085,000	54,876,000
Net realized gains	17,520,000	63,624,000	6,970,000
Other-than-temporary-impairment (OTTI) losses on investments	0	(217,000)	(2,559,000)
Net unrealized gains (losses) on equity securities	78,090,000	(98,735,000)
Consolidated revenue	1,003,591,000	818,123,000	797,224,000
Losses and settlement expenses	413,416,000	428,193,000	401,584,000
Policy acquisition costs	288,697,000	267,738,000	252,515,000
Insurance operating expenses	69,430,000	53,803,000	56,994,000
Interest expense on debt	7,588,000	7,437,000	7,426,000
General corporate expenses	12,686,000	9,427,000	11,340,000
Total expenses	791,817,000	766,598,000	729,859,000
Equity in earnings of unconsolidated investees	20,960,000	16,056,000	17,224,000
Earnings before income taxes	232,734,000	67,581,000	84,589,000
Income tax expense:
Current	26,426,000	23,917,000	9,302,000
Deferred income tax expense (benefit)	14,666,000	(20,515,000)	(29,741,000)
Income tax expense	41,092,000	3,402,000	(20,439,000)
Net earnings	191,642,000	64,179,000	105,028,000
Other comprehensive earnings (loss), net of tax	67,045,000	(33,997,000)	35,309,000
Comprehensive earnings	$ 258,687,000	$ 30,182,000	$ 140,337,000
Basic:
Net earnings per share (in dollars per share)	$ 4.28	$ 1.45	$ 2.39
Comprehensive earnings per share (in dollars per share)	5.78	0.68	3.19
Diluted:
Net earnings per share (in dollars per share)	4.23	1.43	2.36
Comprehensive earnings per share (in dollars per share)	$ 5.72	$ 0.67	$ 3.15
Weighted average number of common shares outstanding
Basic (in shares)	44,734	44,358	44,033
Diluted (in shares)	45,257	44,835	44,500
Cash dividends paid per common share	$ 1.91	$ 1.87	$ 2.58