SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF PARENT - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Condensed financial statements
Cash Flows From Operating Activities	$ 117,799	$ 115,584	$ 122,170
Cash Flows From Investing Activities:
Net Cash Provided by (Used in) Investing Activities	(167,102)	(145,092)	(131,610)
Cash Flows From Financing Activities:
Proceeds from stock option exercises			30
Dividends paid	(56,356)	(51,689)	(47,206)
Net Cash Provided by (Used in) Financing Activities	50,337	(2,266)	44,843
Net change in cash and cash equivalents	1,034	(31,774)	35,403
Cash and cash equivalents, beginning of period	4,963
Cash and cash equivalents, end of year	5,997	4,963
Parent Company
Condensed financial statements
Cash Flows From Operating Activities	56,398	36,799	47,307
Cash Flows From Investing Activities:
Loans (made to)/repaid from, wholly-owned subsidiaries	(81,000)	(46,000)	151,000
Increase in investment of subsidiary	0	0	(60,000)
Net Cash Provided by (Used in) Investing Activities	(81,000)	(46,000)	91,000
Cash Flows From Financing Activities:
Proceeds from stock option exercises	0	0	30
Net change in notes payable to banks	81,000	60,500	(91,000)
Proceeds from note payable to GSWC	0	(26,000)	(6,000)
Repayment of note payable to GSWC	0	26,000	6,000
Dividends paid	(56,356)	(51,689)	(47,206)
Net Cash Provided by (Used in) Financing Activities	24,644	8,811	(138,176)
Net change in cash and cash equivalents	42	(390)	131
Cash and cash equivalents, beginning of period	51	441	310
Cash and cash equivalents, end of year	$ 93	$ 51	$ 441