Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net income	$ 86,602	$ 92,690	$ 71,632
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	1,012	942	996
Net amortization of investments	8,177	8,659	10,787
Change in investment related allowance for credit losses	(27)
Deferred income taxes	1,657	872	(1,462)
Net realized (gains) losses on investments	(1,132)	80	1,536
Net unrealized (gains) losses on equity securities	(4,204)	(4,758)	2,088
Net realized losses on disposal of assets	58	3
Share-based compensation	3,296	2,351	2,065
Changes in operating assets and liabilities:
Premiums receivable, net	1,193	4,525	11,756
Accrued interest receivable	456	467	438
Deferred policy acquisition costs	1,238	686	517
Amounts held by others	7,856		(7,855)
Other assets	(1,230)	710	1,873
Reserves for loss and loss adjustment expenses	(12,326)	(25,522)	26,564
Unearned premiums	(11,613)	(8,423)	(7,974)
Reinsurance balances	(10,333)	16,093	(21,873)
Amounts held for others and policyholder deposits	2,271	(5,528)	2,911
Federal income taxes payable	(2,803)	(192)	5,173
Accounts payable and other liabilities	(6,750)	(4,831)	(904)
Net cash provided by operating activities	63,398	78,824	98,268
Investing activities
Purchases of investments held-to-maturity	(96,452)	(152,133)	(99,330)
Purchases of investments available-for-sale	(73,923)	(63,513)	(124,128)
Purchases of equity securities	(11,330)	(4,495)	(11,459)
Purchases of short-term investments	(139,242)	(125,763)	(133,355)
Proceeds from maturities of investments held-to-maturity	104,564	159,702	99,984
Proceeds from sales and maturities of investments available-for-sale	110,700	114,869	100,357
Proceeds from sales of equity securities			3
Proceeds from sales and maturities of short-term investments	149,975	84,039	139,865
Proceeds from redemptions of other investments			130
Purchases of property and equipment	(921)	(1,018)	(1,126)
Net cash provided by (used in) investing activities	43,371	11,688	(29,059)
Financing activities
Proceeds from stock option exercises		20	67
Finance lease purchases	(50)	(47)
Dividends to shareholders	(88,775)	(87,016)	(84,491)
Net cash used in financing activities	(88,825)	(87,043)	(84,424)
Change in cash and cash equivalents	17,944	3,469	(15,215)
Cash and cash equivalents at beginning of year	43,813	40,344	55,559
Cash and cash equivalents at end of year	61,757	43,813	40,344
Supplemental disclosure of cash flow information
Income taxes paid	$ 20,562	$ 20,850	$ 11,235