Schedule I - Condensed Financial Information Of Registrant (Unconsolidated Statements Of Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Financial Statements, Captions [Line Items]
Interest Paid, Excluding Capitalized Interest, Operating Activities	$ 118,052	$ 122,938	$ 117,457
Net income	119,182	109,967	132,393
Amortization of debt issuance costs and discounts	(3,915)	(3,942)	(4,109)
Increase (Decrease) in Accounts Payable	21,417	(20,322)	3,047
Accrued and other current liabilities	(21,680)	(8,214)	4,413
Other - net	8,355	(340)	(7,357)
Net cash provided by operating activities	225,217	295,425	397,815
Payments for (Proceeds from) Other Investing Activities	(688)	118	278
Net cash used in investing activities	(368,715)	(275,769)	(237,448)
Long-term borrowings, net of discount	95,000	564,568	0
Retirement of long-term debt	(95,000)	(562,135)	0
Distributions to shareholders	(131,476)	(108,739)	(136,426)
Other - net	95	117	152
Net cash provided by (used in) financing activities	123,793	(41,586)	(145,414)
Income Taxes Paid, Net	27,500	27,000	29,600
Accrued taxes payable/receivable	638	6,695	(15,698)
Accrued interest	(1,099)	(3,601)	544
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	6,917	26,622	48,552	$ 33,599
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	(19,705)	(21,930)	14,953
Proceeds from Contributed Capital	275,000	0	0
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Interest Paid, Excluding Capitalized Interest, Operating Activities	35,172	38,069	28,911
Net income	115,969	106,754	129,180
Equity in earnings of subsidiaries	(147,030)	(140,030)	(154,078)
Cash dividends received from subsidiary companies	155,700	147,600	159,000
Amortization of debt issuance costs and discounts	(1,379)	(1,607)	(1,847)
Deferred income taxes - net	(5)	(224)	157
Charges related to early extinguishment of debt	0	2,415	0
Increase (Decrease) in Accounts Payable	(85)	299	231
Accrued and other current liabilities	0	0	(3)
Other - net	4,265	5,005	(623)
Net cash provided by operating activities	133,133	109,026	135,448
Investment in subsidiaries	(275,000)	0	0
Payments for (Proceeds from) Other Investing Activities	0	0	278
Net cash used in investing activities	(275,000)	0	278
Long-term borrowings, net of discount	0	474,568	0
Retirement of long-term debt	0	(472,135)	0
Distributions to shareholders	(131,476)	(108,739)	(136,426)
Other - net	62	6,122	0
Net cash provided by (used in) financing activities	137,352	(106,318)	(136,426)
Income Taxes Paid, Net	27,500	27,000	29,600
Accrued taxes payable/receivable	2,940	(11,317)	(261)
Accrued interest	0	(3,083)	(2)
Repayments of Loans to Subsidiary	(6,110)	20,000	0
Loans from Subsidiary	0	26,110	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1,902	6,417	3,709	$ 4,409
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	(4,515)	2,708	(700)
Proceeds from Contributed Capital	$ 275,000	$ 0	$ 0