Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Gross written premiums	$ 374,930	$ 354,062	$ 1,201,372	$ 1,129,993
Revenues:
Net written premiums	277,001	251,939	903,356	799,141
Change in unearned premiums	7,009	2,143	(86,996)	(66,599)
Net earned premiums	284,010	254,082	816,360	732,542
Net investment income	19,875	17,371	59,344	50,219
Total other-than-temporary impairment losses	23	(1,298)	(248)	(1,747)
Portion of loss recognized in other comprehensive income (before tax)	(23)	23	98	49
Net other-than-temporary impairment losses recognized in earnings		(1,275)	(150)	(1,698)
Net realized gains (losses)	1,586	518	5,143	10,453
Other income (expenses)	(183)	(2,518)	6,796	(4,638)
Total revenues	305,288	268,178	887,493	786,878
Expenses:
Net losses and loss adjustment expenses	172,793	146,546	492,955	418,717
Commission expenses	42,611	34,253	120,891	98,638
Other operating expenses	56,137	56,599	176,020	164,297
Interest expense	3,859	3,856	11,575	11,567
Total expenses	275,400	241,254	801,441	693,219
Income before income taxes	29,888	26,924	86,052	93,659
Income tax expense (benefit)	7,875	8,723	24,917	30,345
Net income	$ 22,013	$ 18,201	$ 61,135	$ 63,314
Net income per common share:
Basic	$ 1.51	$ 1.26	$ 4.21	$ 4.40
Diluted	$ 1.46	$ 1.23	$ 4.08	$ 4.29
Average common shares outstanding:
Basic	14,557,376	14,411,927	14,528,917	14,384,291
Diluted	15,070,422	14,811,095	14,998,385	14,767,949