SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments other than subsidiaries [Abstract]
Fixed maturities												$ 491,904	$ 437,184
Limited partnerships												76,469	75,458
Total Investments												689,818	660,360
Cash and cash equivalents	$ 62,976			$ 73,538	$ 73,538			$ 64,632	$ 62,976	$ 73,538	$ 64,632	62,976	73,538	$ 64,632	$ 59,297
Accounts receivable												64,984	66,522
Other assets												23,779	11,009
Total Assets												1,154,137	1,085,771
Liabilities [Abstract]
Total Liabilities												749,792	691,273
Shareholders' equity [Abstract]
Additional paid-in capital												54,286	52,946
Unrealized net gains on investments												34,051	38,924
Foreign exchange adjustment												(831)	(1,066)
Retained earnings												316,195	303,053	294,773	280,003
Shareholders' equity												404,345	394,498	399,496	381,724
Total liabilities and shareholders' equity												1,154,137	1,085,771
Revenue [Abstract]
Net investment income	3,982	$ 3,513	$ 3,549	3,440	3,771	$ 3,014	$ 2,898	2,815	14,483	12,498	9,055
Net realized losses on investments									23,228	(1,261)	14,930
Total revenue									318,997	280,275	292,042
Expenses [Abstract]
Other									89,462	90,573	88,048
Total expenses									275,943	246,323	247,644
Income before federal income taxes and equity in undistributed income of subsidiaries									43,054	33,952	44,398
Federal income tax benefit									14,109	10,669	14,681
Equity in undistributed income of subsidiaries									2,473	(1,687)	7,108
Net income	4,864	$ 4,001	$ 5,969	14,112	3,541	$ 7,780	$ 5,718	6,243	28,945	23,283	29,717
Condensed Statements of Cash Flows [Abstract]
Net cash provided by operating activities									32,368	38,197	30,160
Investing activities [Abstract]
Net sales of short-term investments									11,258	746	1,925
Distributions from limited partnerships									1,462	4,494	1,752
Net cash used in investing activities									(27,362)	(12,832)	(18,867)
Financing activities [Abstract]
Dividends paid to shareholders									(15,803)	(15,003)	(14,947)
Net cash used in financing activities									(15,803)	(15,003)	(4,947)
Increase (decrease) in cash and cash equivalents									(10,562)	8,906	5,335
Cash and cash equivalents at beginning of year				73,538				64,632	73,538	64,632	59,297
Cash and cash equivalents at end of year	62,976				73,538				62,976	73,538	64,632
Class A [Member]
Shareholders' equity [Abstract]
Common stock												112	112
Class B [Member]
Shareholders' equity [Abstract]
Common stock												532	529
Parent Company [Member]
Assets [Abstract]
Investment in subsidiaries												409,892	405,192
Due from affiliates												3,381	2,945
Investments other than subsidiaries [Abstract]
Fixed maturities												10,166	12,181
Limited partnerships												205	208
Total Investments												10,371	12,389
Cash and cash equivalents	14,995			17,934	17,934			16,615	17,934	17,934	16,615	14,995	17,934	$ 16,615	$ 9,848
Accounts receivable												7,602	6,418
Other assets												25,763	21,067
Total Assets												472,004	465,945
Liabilities [Abstract]
Premiums payable												11,973	21,672
Deposits from insureds												30,087	23,484
Short-term borrownings												20,000	20,000
Other liabilities												5,599	6,291
Total Liabilities												67,659	71,447
Shareholders' equity [Abstract]
Additional paid-in capital												54,286	52,946
Unrealized net gains on investments												34,051	38,924
Foreign exchange adjustment												(831)	(1,066)
Retained earnings												316,195	303,053
Shareholders' equity												404,345	394,498
Total liabilities and shareholders' equity												472,004	465,945
Revenue [Abstract]
Commissions and service fees									27,736	23,523	22,153
Cash dividends from subsidiaries									20,000	20,000	15,000
Net investment income									134	120	102
Net realized losses on investments									(3)	(22)	(27)
Other									(24)	(17)	126
Total revenue									47,843	43,604	37,354
Expenses [Abstract]
Salary and related items									17,462	17,616	15,543
Other									10,808	7,297	7,978
Total expenses									28,270	24,913	23,521
Income before federal income taxes and equity in undistributed income of subsidiaries									19,573	18,691	13,833
Federal income tax benefit									(69)	(350)	(294)
Income before equity in undistributed income of subsidiaries									19,642	19,041	14,127
Equity in undistributed income of subsidiaries									9,303	4,242	15,590
Net income									28,945	23,283	29,717
Condensed Statements of Cash Flows [Abstract]
Net cash provided by operating activities									15,484	21,841	19,719
Investing activities [Abstract]
Purchases of long-term investments									(4,000)	(4,792)	(6,398)
Sales or maturities of long-term investments									3,493	4,194	5,253
Net sales of short-term investments									2,165	0	0
Distributions from limited partnerships									0	0	13
Net purchases of property and equipment									(4,278)	(4,921)	(6,873)
Net cash used in investing activities									(2,620)	(5,519)	(8,005)
Financing activities [Abstract]
Dividends paid to shareholders									(15,803)	(15,003)	(14,947)
Drawings on line of credit									0	0	10,000
Net cash used in financing activities									(15,803)	(15,003)	(4,947)
Increase (decrease) in cash and cash equivalents									(2,939)	1,319	6,767
Cash and cash equivalents at beginning of year				$ 17,934				$ 16,615	17,934	16,615	9,848
Cash and cash equivalents at end of year	$ 14,995				$ 17,934				$ 14,995	$ 17,934	$ 16,615
Parent Company [Member] | Class A [Member]
Shareholders' equity [Abstract]
Common stock												112	112
Parent Company [Member] | Class B [Member]
Shareholders' equity [Abstract]
Common stock												$ 532	$ 529