Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Gross Written Premiums		$ 452,179	$ 412,565	$ 902,484	$ 826,442
Revenues:
Net Written Premiums		333,282	306,535	670,445	626,355
Change in Unearned Premiums		(39,447)	(38,543)	(90,479)	(94,005)
Net Earned Premiums		293,835	267,992	579,966	532,350
Net Investment Income		22,265	19,875	43,713	39,469
Total Other-Than-Temporary Impairment Losses		29	(162)	(1,048)	(271)
Portion of Loss Recognized in Other Comprehensive Income (Before Tax)		(29)	12	(45)	121
Net Other-Than-Temporary Impairment Losses Recognized in Earnings		0	(150)	(1,093)	(150)
Net Realized Gains		1,694	1,960	2,743	3,557
Other Income (Loss)		(411)	4,430	657	6,979
Total Revenues		317,383	294,107	625,986	582,205
Expenses:
Net Losses and Loss Adjustment Expenses		177,110	167,206	346,710	320,162
Commission Expenses		48,173	40,726	96,017	78,280
Other Operating Expenses		60,766	59,074	119,304	119,883
Interest Expense		3,861	3,858	7,722	7,716
Total Expenses		289,910	270,864	569,753	526,041
Income Before Income Taxes		27,473	23,243	56,233	56,164
Income Tax Expense		6,971	7,053	14,621	17,042
Net Income		$ 20,502	$ 16,190	$ 41,612	$ 39,122
Net income per common share:
Basic	[1]	$ 0.70	$ 0.56	$ 1.42	$ 1.35
Diluted	[1]	$ 0.69	$ 0.54	$ 1.39	$ 1.31
Average common shares outstanding:
Basic	[1]	29,470	29,074	29,377	29,029
Diluted	[1]	29,918	29,953	29,897	29,884
Cash Dividends Declared per Common Share		$ 0.06	$ 0.045	$ 0.105	$ 0.045

[1] We completed a two-for-one stock split on January 20, 2017. All share and per share data prior to January 20, 2017 has been retroactively restated on a post-split basis.