Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Cash Flows [Abstract]
Net cash provided by (used in) operating activities	$ 60,287	$ (5,767)
Purchase of:
Fixed income securities, available-for-sale	(145,121)	(69,233)
Equity securities	(31,957)	(31,811)
Property and equipment	(887)	(1,910)
Other	(4,323)	(2,611)
Proceeds from sale of:
Fixed income securities, available-for-sale	21,300	20,414
Equity securities	47,638	38,042
Other	521	2,267
Proceeds from call or maturity of:
Fixed income securities, available-for-sale	96,285	54,890
Net cash provided by (used in) investing activities	(16,544)	10,048
Cash Flows from Financing Activities
Cash dividends paid	(10,838)	(10,332)
Proceeds from (payments related to) stock option exercises	(187)	2,549
Net cash used in financing activities	(11,025)	(7,783)
Net increase (decrease) in cash	32,718	(3,502)
Cash at the beginning of the period	62,217	46,203
Cash at the end of the period	$ 94,935	$ 42,701