Schedule II Financial Information of Registrant - Parent Company Statement of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net cash provided by (used in) operating activities (1)	$ 658,434	$ 694,431	$ 677,786
Cash flows from investing activities:
Proceeds from sales of Fixed-maturity investments available-for-sale	963,589	986,647	728,584
Proceeds from sales of Trading securities	11,602	130,537	58,317
Proceeds from sales of Equity securities	90,450	69,779	95,697
Proceeds from redemptions of Fixed-maturity investments available for sale	645,068	464,777	457,595
Proceeds from redemptions of Trading securities	22,913	37,684	54,329
Purchases of Fixed-maturity investments available for sale	(2,449,762)	(1,913,703)	(1,875,069)
Sales, redemptions and (purchases) of Short-term investments, net	(82,925)	8,017	(108,325)
Sales, redemptions and (purchases) of Other assets, net	(1,434)	739	(2,590)
Net cash provided by (used in) investing activities	(883,180)	(302,049)	(689,414)
Cash flows from financing activities:
Dividends and dividend equivalents paid	(97,458)	(2,061)	(2,140)
Issuance of senior notes, net	515,567	442,439	0
Repayments and repurchases of senior notes	0	(610,763)	0
Issuance of common stock	1,553	2,416	1,385
Repurchases of common shares	(226,305)	(300,201)	(50,053)
Proceeds from (Payments for) Other Financing Activities	(2,292)	(989)	(1,510)
Net cash provided by (used in) financing activities	222,618	(403,106)	22,386
Effect of exchange rate changes on cash and restricted cash	0	(4)	0
Increase (decrease) in cash and restricted cash	(2,128)	(10,728)	10,758
Cash and restricted cash, beginning of period	96,274	107,002	96,244
Cash and restricted cash, end of period	94,146	96,274	107,002
Parent Company
Cash flows from operating activities:
Net cash provided by (used in) operating activities (1)	(13,741)	143,664	254,698
Cash flows from investing activities:
Proceeds from sales of Fixed-maturity investments available-for-sale	304,737	296,171	6,779
Proceeds from sales of Trading securities	0	56,787	0
Proceeds from sales of Equity securities	13,401	16,916	0
Proceeds from redemptions of Fixed-maturity investments available for sale	238,161	149,767	12,391
Proceeds from redemptions of Trading securities	0	114	0
Purchases of Fixed-maturity investments available for sale	(691,874)	(293,284)	(37,552)
Sales, redemptions and (purchases) of Short-term investments, net	(53,024)	157,045	(131,164)
Sales, redemptions and (purchases) of Other assets, net	(6,068)	(6,958)	(3,317)
Capital distributions from subsidiaries	19,000	6,000	0
Capital contributions to subsidiaries	(5,050)	(65,879)	(30,338)
Net cash provided by (used in) investing activities	(180,717)	316,679	(183,201)
Cash flows from financing activities:
Dividends and dividend equivalents paid	(97,458)	(2,061)	(2,140)
Issuance of senior notes, net	515,567	442,439	0
Repayments and repurchases of senior notes	0	(610,763)	0
Issuance of common stock	1,553	2,416	1,385
Repurchases of common shares	(226,305)	(300,201)	(50,053)
Proceeds from (Payments for) Other Financing Activities	(2,292)	(989)	(1,510)
Net cash provided by (used in) financing activities	191,065	(469,159)	(52,318)
Effect of exchange rate changes on cash and restricted cash	0	(2)	0
Increase (decrease) in cash and restricted cash	(3,393)	(8,818)	19,179
Cash and restricted cash, beginning of period	23,534	32,352	13,173
Cash and restricted cash, end of period	20,141	23,534	32,352
Cash Distributions Received From Consolidated Subsidiaries	1,700	26,600	55,400
Dividends Received From Consolidated Subsidiaries	$ 484,100	$ 362,400	$ 394,600