Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Statement Of Cash Flows [Abstract]
Net cash provided by operating activities	$ 163,244	$ 186,762
Purchase of:
Fixed income securities, available-for-sale	(368,586)	(380,813)
Equity securities	(62,643)	(73,072)
Property and equipment	(4,969)	(4,056)
Other	(15,095)	(12,154)
Proceeds from sale of:
Fixed income securities, available-for-sale	68,229	173,120
Equity securities	66,185	47,799
Other	3,136	2,057
Proceeds from call or maturity of:
Fixed income securities, available-for-sale	199,036	106,241
Net proceeds from sale (purchase) of short-term investments		6,016
Net cash used in investing activities	(114,707)	(134,862)
Cash Flows from Financing Activities
Cash dividends paid	(31,931)	(30,428)
Proceeds from stock option exercises	7,780	12,436
Net cash used in financing activities	(24,151)	(17,992)
Net increase in cash	24,386	33,908
Cash at the beginning of the period	46,203	30,140
Cash at the end of the period	$ 70,589	$ 64,048

Cash inflow (outflow) from stock option exercises.

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Represents the amount of net cash outflow from other investing activities.

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Payments to Acquire Investments and Productive Assets [Abstract]

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Proceeds from Sale of Investments and Productive Assets [Abstract]

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Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of increase (decrease) in cash, cash equivalents, and cash and cash equivalents restricted to withdrawal or usage; including effect from exchange rate change. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

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Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

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The net amount paid (received) by the reporting entity through acquisition or sale and maturities of short-term investments with an original maturity that is three months or less which qualify for treatment as an investing activity based on management's intention and intended by management to be liquidated, if necessary, within the current operating cycle. Includes cash flows from securities classified as trading securities that were acquired for reasons other than sale in the short-term.

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Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity.

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Amount of cash outflow to acquire investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of cash outflow for purchase of marketable security.

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The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

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Amount of cash inflow from maturity, prepayment and call of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities (held-to-maturity or available-for-sale) during the period.

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