Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Gross written premiums	$ 412,565	$ 379,471	$ 826,442	$ 775,931
Revenues:
Net written premiums	306,535	258,244	626,355	547,202
Change in unearned premiums	(38,543)	(15,916)	(94,005)	(68,742)
Net earned premiums	267,992	242,328	532,350	478,460
Net investment income	19,875	16,595	39,469	32,848
Total other-than-temporary impairment losses	(162)	(472)	(271)	(450)
Portion of loss recognized in other comprehensive income (before tax)	12	49	121	27
Net other-than-temporary impairment losses recognized in earnings	(150)	(423)	(150)	(423)
Net realized gains (losses)	1,960	4,339	3,557	9,935
Other income (expenses)	4,430	(4,362)	6,979	(2,120)
Total revenues	294,107	258,477	582,205	518,700
Expenses:
Net losses and loss adjustment expenses	167,206	141,973	320,162	272,171
Commission expenses	40,726	31,480	78,280	64,385
Other operating expenses	59,074	52,789	119,883	107,698
Interest expense	3,858	3,856	7,716	7,711
Total expenses	270,864	230,098	526,041	451,965
Income before income taxes	23,243	28,379	56,164	66,735
Income tax expense (benefit)	7,053	9,195	17,042	21,622
Net income	$ 16,190	$ 19,184	$ 39,122	$ 45,113
Net income per common share:
Basic	$ 1.11	$ 1.33	$ 2.70	$ 3.14
Diluted	$ 1.08	$ 1.30	$ 2.62	$ 3.06
Average common shares outstanding:
Basic	14,536,849	14,396,048	14,514,532	14,370,123
Diluted	14,976,593	14,763,002	14,942,193	14,726,282