Segment Information - Schedule of Segment Reporting Information by Segment (Detail) - USD ($)		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Revenues, Unaffiliated Customers
Total intersegment revenues		$ 670,604,000	$ 680,704,000	$ 569,968,000
Intersegment Revenues (1)
Total intersegment revenues		670,604,000	680,704,000	569,968,000
Operating Income
Operating Income		150,803,000	142,933,000	131,112,000
Other income		1,438,000	5,051,000	1,720,000
Interest charges		36,951,000	24,356,000	20,135,000
Income Before Income taxes		115,290,000	123,628,000	112,697,000
Income taxes		28,078,000	33,832,000	29,231,000
Net Income		87,212,000	89,796,000	83,466,000
Depreciation and Amortization
Total depreciation and amortization		65,501,000	68,973,000	62,661,000
Identifiable Assets
Total identifiable assets		3,304,704,000	2,215,037,000
RSAM Adjustment		5,100,000
Florida City Gas
Identifiable Assets
Business Combination, Consideration Transferred		923,400,000
Regulated Energy
Operating Income
Operating Income		126,199,000	115,317,000	106,174,000
Depreciation and Amortization
Total depreciation and amortization		48,162,000	52,707,000	48,748,000
Payments to Acquire Productive Assets		1,095,871,000	97,554,000	139,733,000
Regulated Energy | Florida City Gas
Operating Revenues, Unaffiliated Customers
Total intersegment revenues		12,100,000
Intersegment Revenues (1)
Total intersegment revenues		12,100,000
Operating Income
Operating Income		(3,300,000)
Unregulated Energy
Operating Income
Operating Income		24,426,000	27,350,000	24,427,000
Depreciation and Amortization
Total depreciation and amortization		17,347,000	16,257,000	13,869,000
Payments to Acquire Productive Assets		40,264,000	40,773,000	81,651,000
Other
Operating Income
Operating Income		178,000	266,000	511,000
Depreciation and Amortization
Payments to Acquire Productive Assets		1,762,000	2,355,000	6,425,000
Other and eliminations
Depreciation and Amortization
Total depreciation and amortization		(8,000)	9,000	44,000
Total for Segments [Member]
Depreciation and Amortization
Payments to Acquire Productive Assets		1,137,897,000	140,682,000	227,809,000
Operating Segments
Operating Revenues, Unaffiliated Customers
Total intersegment revenues		670,604,000	680,704,000	569,968,000
Intersegment Revenues (1)
Total intersegment revenues		670,604,000	680,704,000	569,968,000
Operating Segments | Regulated Energy
Operating Revenues, Unaffiliated Customers
Total intersegment revenues		471,591,000	422,894,000	381,879,000
Intersegment Revenues (1)
Total intersegment revenues		471,591,000	422,894,000	381,879,000
Identifiable Assets
Total identifiable assets		2,781,581,000	1,716,255,000
Operating Segments | Unregulated Energy
Operating Revenues, Unaffiliated Customers
Total intersegment revenues		199,013,000	257,810,000	188,089,000
Intersegment Revenues (1)
Total intersegment revenues		199,013,000	257,810,000	188,089,000
Identifiable Assets
Total identifiable assets		477,402,000	463,239,000
Intersegment Eliminations
Operating Revenues, Unaffiliated Customers
Total intersegment revenues	[1]	26,321,000	29,778,000	21,348,000
Intersegment Revenues (1)
Total intersegment revenues	[1]	26,321,000	29,778,000	21,348,000
Intersegment Eliminations | Regulated Energy
Operating Revenues, Unaffiliated Customers
Total intersegment revenues		2,004,000	6,530,000	2,041,000
Intersegment Revenues (1)
Total intersegment revenues		2,004,000	6,530,000	2,041,000
Intersegment Eliminations | Unregulated Energy
Operating Revenues, Unaffiliated Customers
Total intersegment revenues		24,135,000	22,940,000	18,780,000
Intersegment Revenues (1)
Total intersegment revenues		24,135,000	22,940,000	18,780,000
Intersegment Eliminations | Other
Operating Revenues, Unaffiliated Customers
Total intersegment revenues		182,000	308,000	527,000
Intersegment Revenues (1)
Total intersegment revenues		182,000	308,000	$ 527,000
Other And Intersegment Eliminations
Identifiable Assets
Total identifiable assets		$ 45,721,000	$ 35,543,000

[1] All significant intersegment revenues are billed at market rates and have been eliminated from consolidated revenues.  (2) Depreciation and amortization in 2023 includes a $5.1 million RSAM adjustment. See Note 18 for additional details.  (3) Capital expenditures in 2023 include our acquisition of FCG for $923.4 million. See Note 4 for additional details.