Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net income	$ 46,231	$ 77,865	$ 70,462
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	984	1,181	1,348
Net amortization of investments	14,015	16,247	16,424
Deferred income taxes	12,800	(2,249)	1,446
Net realized losses on investments	647	509	2,494
Net realized losses on disposal of assets	2	1	664
Share-based compensation	2,018	1,603	1,223
Changes in operating assets and liabilities:
Premiums receivable, net	8,771	2,359	(6,447)
Accrued interest receivable	725	325	(48)
Deferred policy acquisition costs	(951)	1,112	(763)
Amounts held by others	27,848	1,016	(27,847)
Other assets	(1,882)	1,631	(1,042)
Reserves for loss and loss adjustment expenses	29,069	24,743	30,431
Unearned premiums	(4,758)	(5,955)	(593)
Reinsurance balances	(6,495)	7,285	(5,878)
Amounts held for others and policyholder deposits	4,168	(17,066)	6,621
Accounts payable and other liabilities	(2,382)	3,605	4,364
Net cash provided by operating activities	130,810	114,212	92,859
Investing activities
Purchases of investments held-to-maturity	(222,104)	(102,830)	(178,010)
Purchases of investments available-for-sale	(117,020)	(216,466)	(135,915)
Purchases of short-term investments	(62,687)	(35,295)	(12,246)
Proceeds from maturities of investments held-to-maturity	152,995	177,159	160,834
Proceeds from sales and maturities of investments available-for-sale	112,180	115,552	78,637
Proceeds from sales and maturities of short-term investments	72,400	13,040	37,833
Proceeds from redemptions of other investments	13,172
Purchases of property and equipment	(478)	(1,638)	(953)
Net cash used in investing activities	(51,542)	(50,478)	(49,820)
Financing activities
Proceeds from stock option exercises		837	1,844
Tax benefit from share-based payments		995	2,203
Dividends to shareholders	(82,645)	(76,111)	(68,561)
Net cash used in financing activities	(82,645)	(74,279)	(64,514)
Change in cash and cash equivalents	(3,377)	(10,545)	(21,475)
Cash and cash equivalents at beginning of year	58,936	69,481	90,956
Cash and cash equivalents at end of year	55,559	58,936	69,481
Supplemental disclosure of cash flow information
Income taxes paid	$ 28,255	$ 31,500	$ 23,851