Schedule II - Condensed Financial Information of Registrant (Parent Company) - Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
ASSETS
Cash	$ 88,804	$ 62,217
Investment in unconsolidated investees	171,311	128,382
Fixed income:
Available-for-sale, at fair value (amortized cost of $84,823 and allowance for credit losses of $0 in 2021) (amortized cost of $60,657 and allowance for credit losses of $0 in 2020)	2,409,887	2,196,626
Property and equipment, at cost, net of accumulated depreciation of $1,697 in 2021 and $1,629 in 2020	52,161	51,406
TOTAL ASSETS	4,508,302	3,938,485
LIABILITIES
Bonds payable, long-term debt	199,700
TOTAL LIABILITIES	3,278,941	2,802,507
SHAREHOLDERS' EQUITY
Common stock ($0.01 par value) (Shares authorized - 200,000,000) (68,219,551 shares issued and 45,289,337 shares outstanding in 2021) (68,072,794 shares issued and 45,142,580 shares outstanding in 2020)	682	681
Paid-in capital	343,742	335,365
Accumulated other comprehensive earnings	49,826	108,714
Retained earnings	1,228,110	1,084,217
Deferred compensation	9,642	8,292
Treasury stock, at cost (22,930,214 shares in 2021 and 2020)	(402,641)	(401,291)
TOTAL SHAREHOLDERS' EQUITY	1,229,361	1,135,978	$ 995,388	$ 806,842
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	4,508,302	3,938,485
Parent Company
ASSETS
Cash	1,433	381
Accounts receivable, affiliates	848
Investments in subsidiaries	1,197,997	1,148,342
Investment in unconsolidated investees	113,052	90,893
Fixed income:
Available-for-sale, at fair value (amortized cost of $84,823 and allowance for credit losses of $0 in 2021) (amortized cost of $60,657 and allowance for credit losses of $0 in 2020)	86,483	64,211
Property and equipment, at cost, net of accumulated depreciation of $1,697 in 2021 and $1,629 in 2020	1,711	1,779
Income taxes receivable - current	211	1,500
Other assets	2,907	895
TOTAL ASSETS	1,404,642	1,308,001
LIABILITIES
Accounts payable, affiliates		2,556
Income taxes - deferred	21,067	16,988
Bonds payable, long-term debt	149,676	149,489
Interest payable, long-term debt	2,153	2,153
Other liabilities	2,385	837
TOTAL LIABILITIES	175,281	172,023
SHAREHOLDERS' EQUITY
Common stock ($0.01 par value) (Shares authorized - 200,000,000) (68,219,551 shares issued and 45,289,337 shares outstanding in 2021) (68,072,794 shares issued and 45,142,580 shares outstanding in 2020)	682	681
Paid-in capital	343,742	335,365
Accumulated other comprehensive earnings	49,826	108,714
Retained earnings	1,228,110	1,084,217
Deferred compensation	9,642	8,292
Treasury stock, at cost (22,930,214 shares in 2021 and 2020)	(402,641)	(401,291)
TOTAL SHAREHOLDERS' EQUITY	1,229,361	1,135,978
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 1,404,642	$ 1,308,001