Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Gross Written Premiums	$ 1,912,961	$ 1,713,265	$ 1,568,911
Revenues:
Net Written Premiums	1,471,085	1,271,330	1,186,224
Change in Net Unearned Premiums	(107,862)	(84,910)	(85,879)
Net Earned Premiums	1,363,223	1,186,420	1,100,345
Net Investment Income	103,113	89,293	79,451
Net Realized and Unrealized Gains (Losses):
Total Other-Than-Temporary Impairment Losses	(118)	(2,002)	(227)
Portion of Loss Recognized in Other Comprehensive Income	118	(62)	77
Net Other-Than-Temporary Impairment Losses Recognized in Earnings	0	(2,064)	(150)
Net Realized Gains on Investments Sold	2,989	45,073	9,186
Net Unrealized Losses on Equity Securities	(33,337)	0	0
Total Net Realized and Unrealized Gains (Losses)	(30,348)	43,009	9,036
Other Income (Loss)	7,169	(4,243)	8,701
Total Revenues	1,443,157	1,314,479	1,197,533
Expenses:
Net Losses and Loss Adjustment Expenses	893,779	806,265	665,448
Commission Expenses	220,144	184,731	165,045
Other Operating Expenses	261,224	233,230	234,096
Merger Transaction Costs	3,950	0	0
Interest Expense	15,485	15,447	15,435
Total Expenses	1,394,582	1,239,673	1,080,024
Income Before Income Taxes	48,575	74,806	117,509
Income Tax Expense	14,336	34,312	34,783
Net Income	$ 34,239	$ 40,494	$ 82,726
Net Income Per Common Share:
Basic	$ 1.15	$ 1.38	$ 2.85
Diluted	$ 1.13	$ 1.35	$ 2.75
Average Common Shares Outstanding:
Basic	29,720	29,441	29,074
Diluted	30,193	30,071	30,032