Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Gross written premiums	$ 354,062	$ 327,469	$ 1,129,993	$ 1,099,054
Revenues:
Net written premiums	251,939	228,417	799,141	772,131
Change in unearned premiums	2,143	16,950	(66,599)	(70,408)
Net earned premiums	254,082	245,367	732,542	701,723
Net investment income	17,371	15,839	50,219	48,097
Net realized gains (losses):
Total other-than-temporary impairment losses	(1,298)	(41)	(1,747)	158
Portion of loss recognized in other comprehensive income (before tax)	23	41	49	(158)
Net other-than-temporary impairment losses recognized in earnings	(1,275)	0	(1,698)	0
Other realized gains (losses)	518	6,718	10,453	12,024
Net realized gains (losses)	(757)	6,718	8,755	12,024
Other income (loss)	(2,518)	1,336	(4,638)	10,070
Total revenues	268,178	269,260	786,878	771,914
Expenses:
Net losses and loss adjustment expenses	146,546	135,284	418,717	410,571
Commission expenses	34,253	33,943	98,638	91,820
Other operating expenses	56,599	50,388	164,297	145,526
Interest expense	3,856	3,388	11,567	11,559
Total expenses	241,254	223,003	693,219	659,476
Income before income taxes	26,924	46,257	93,659	112,438
Income tax expense	8,723	15,032	30,345	36,384
Net income	$ 18,201	$ 31,225	$ 63,314	$ 76,054
Net income per common share:
Basic	$ 1.26	$ 2.19	$ 4.40	$ 5.34
Diluted	$ 1.23	$ 2.14	$ 4.29	$ 5.22
Average common shares outstanding:
Basic	14,411,927	14,265,260	14,384,291	14,252,910
Diluted	14,811,095	14,613,744	14,767,949	14,577,297