Consolidated Statements of Income (Loss) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Gross Written Premiums	$ 495,224	$ 450,305
Revenues:
Net Written Premiums	393,262	337,163
Change in Unearned Premiums	(70,635)	(51,032)
Net Earned Premiums	322,627	286,131
Net Investment Income	23,702	21,448
Net Realized and Unrealized Gains (Losses):
Total Other-Than-Temporary Impairment Losses	(37)	(1,077)
Portion of Loss Recognized in Other Comprehensive Income (Before Tax)	37	(16)
Net Other-Than-Temporary Impairment Losses Recognized in Earnings	0	(1,093)
Net Realized Gains on Investments Sold	1,169	1,049
Net Unrealized Losses on Equity Securities at Fair Value	(3,181)
Total Net Realized and Unrealized Losses	(2,012)	(44)
Other Income (Loss)	(117)	1,068
Total Revenues	344,200	308,603
Expenses:
Net Losses and Loss Adjustment Expenses	186,145	169,600
Commission Expenses	54,152	47,844
Other Operating Expenses	62,926	58,538
Interest Expense	3,864	3,861
Total Expenses	307,087	279,843
Income (Loss) Before Income Taxes	37,113	28,760
Income Tax Expense	6,235	7,650
Net Income (Loss)	$ 30,878	$ 21,110
Net Income per Common Share:
Basic	$ 1.04	$ 0.72
Diluted	$ 1.02	$ 0.70
Average common shares outstanding:
Basic	29,595	29,283
Diluted	30,137	30,000
Cash Dividends Declared per Common Share	$ 0.07	$ 0.045