Sch II - Condensed Financial Information on Registrant Cash Flow (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 213,054	$ 239,177	$ 239,634
Equity securities	(16,729)	(4,447)	(2,692)
Short-term investments, net change	3,848	1,294	(659)
Net Cash Provided by (Used in) Investing Activities	(154,611)	(211,892)	(233,318)
Repurchase of common stock, net	(5,346)	(15,152)	356
Dividends paid	(84,474)	(83,128)	(81,401)
Net Cash Provided by (Used in) Financing Activities	(60,201)	(60,946)	12,797
Increase in cash and cash equivalents	(1,758)	(33,661)	19,113
Cash and cash equivalents at end of year	17,277	19,035	52,696
Cash and cash equivalents at beginning of year	19,035	52,696	33,583
Income Taxes Received, Net	2,736	3,005	16,347
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	(107)	(2,102)	417
Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale	3,849	4,641	5,478
Equity securities	(938)	(1,147)	(702)
Short-term investments, net change	530	853	(472)
Dividends from subsidiaries (eliminated in consolidation)	91,300	91,997	71,500
Net Cash Provided by (Used in) Investing Activities	94,741	96,344	75,804
Repurchase of common stock, net	(5,346)	(15,152)	330
Capital contribution by parent to subsidiary	(2,800)	(7,800)	(2,000)
Dividends paid	(84,474)	(83,128)	(81,400)
Net Cash Provided by (Used in) Financing Activities	(92,620)	(106,080)	(83,070)
Increase in cash and cash equivalents	2,014	(11,838)	(6,849)
Cash and cash equivalents at end of year	14,130	12,116	23,954
Cash and cash equivalents at beginning of year	12,116	23,954	30,803
Income Taxes Received, Net	(2,383)	(1,617)	2,849
Cash paid during the period for interest	4,850	4,850	4,850
Dividends in form of cash \| Parent Company
Condensed Financial Statements, Captions [Line Items]
Dividends from subsidiaries (eliminated in consolidation)	$ 91,300	$ 91,997	$ 71,500

Capital contribution by parent to subsidiary, eliminated in consolidation, for parent only financial statements.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of increase (decrease) in cash and cash equivalents. Cash and cash equivalents are the amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes 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. Includes effect from exchange rate changes.

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This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries.

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The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.

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Amount of cash paid for interest, including, but not limited to, capitalized interest and payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount; classified as operating and investing activities.

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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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The cash outflow to acquire equity securities classified as available-for-sale securities, because they are not classified as trading securities.

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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 net cash inflow or outflow resulting from the entity's share transaction.

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