Long-Term Debt - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022		Feb. 01, 2023	Dec. 31, 2021
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount	[1]	$ 170,000
Percentage of equity of total capitalization		40.00%
Fixed charge coverage ratio		1.2
Required net book value of regulated business assets, minimum percentage of consolidated total assets		50.00%
Maximum limit on payment of dividends		$ 10,000
Cumulative consolidated net income base		754,200
Cumulative net income with restrictions		326,400
Long-term debt including current maturities		600,800			$ 568,800
Long-term Debt and Lease Obligation		599,871			567,865
Total long-term debt, net of current maturities		578,388			549,903
Unamortized Debt Issuance Expense		(946)			(913)
Long-term Debt and Lease Obligation, Current		(21,483)			(17,962)
MetLife [Member]
Debt Instrument [Line Items]
Face amount		150,000		$ 200,000
Debt Instrument, Unused Borrowing Capacity, Amount		100,000
Long-term debt including current maturities		50,000
Prudential [Member]
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount	[2]	70,000
Long-term debt including current maturities	[2]	220,000
Prudential [Member] | Maximum [Member]
Debt Instrument [Line Items]
Face amount		$ 370,000	[2]	$ 405,000
Uncollateralized Senior Note Due On Two Thousand Twenty Six [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage		5.68%
Long-term debt including current maturities		$ 11,600			14,500
Uncollateralized Senior Note Due December Two Thousand Thirty Four [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage		2.98%
Long-term debt including current maturities		$ 70,000
Uncollateralized Senior Note Due On May 2 Two Thousand Twenty Eight [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage		6.43%
Long-term debt including current maturities		$ 4,200			4,900
Uncollateralized Senior Note Two Due on December Two Thousand Twenty Eight [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage		3.73%
Long-term debt including current maturities		$ 12,000			14,000
Uncollateralized Senior Notes Due On Two Thousand Twenty Nine [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage		3.88%
Long-term debt including current maturities		$ 35,000			40,000
Uncollateralized Senior Note Due On Two Thousand Twenty Three [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage		5.93%
Long-term debt including current maturities		$ 3,000			6,000
Uncollateralized Senior Note Due April Two Thousand Thirty Two [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage		3.25%
Long-term debt including current maturities		$ 66,500			70,000
Uncollateralized Senior Note Due May Two Thousand Thirty Eight [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage		3.48%
Long-term debt including current maturities		$ 50,000			50,000
Uncollateralized Senior Note Due November Two Thousand Thirty Eight [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage		3.58%
Long-term debt including current maturities		$ 50,000			50,000
Uncollateralized Senior Note Due November Two Thousand Thirty Nine
Debt Instrument [Line Items]
Long-term debt including current maturities		$ 100,000			100,000
Uncollateralized Senior Note Due November Two Thousand Thirty Four
Debt Instrument [Line Items]
Long-term debt including current maturities					70,000
Uncollateralized Senior Note Due July Two Thousand Thirty Five
Debt Instrument [Line Items]
Long-term debt, interest percentage		3.00%
Long-term debt including current maturities		$ 50,000			50,000
Uncollateralized Senior Note Due August Two Thousand Thirty Five
Debt Instrument [Line Items]
Long-term debt, interest percentage		2.96%
Long-term debt including current maturities		$ 40,000			40,000
Uncollateralized Senior Note Due January Two Thousand Thirty Seven
Debt Instrument [Line Items]
Long-term debt, interest percentage		2.49%
Long-term debt including current maturities		$ 50,000			50,000
Equipment Security Note
Debt Instrument [Line Items]
Long-term debt, interest percentage		2.46%
Long-term debt including current maturities		$ 8,517			$ 9,378
Uncollateralized Senior Note Due March 15, 2042
Debt Instrument [Line Items]
Long-term debt, interest percentage		2.95%
Long-term debt including current maturities		$ 50,000
Uncollateralized Senior Note Due March 15, 2042 | MetLife [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		$ 50,000
Uncollateralized Senior Note Due March 14, 2038
Debt Instrument [Line Items]
Long-term debt, interest percentage		5.43%
Long-term debt including current maturities		$ 80,000
Uncollateralized Senior Note Due March 14, 2038 | Prudential [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		80,000
Marlin Gas Services [Member] | Equipment Security Note
Debt Instrument [Line Items]
Long-term debt including current maturities		$ 9,600

[1] 1) The amended Prudential and MetLife Shelf Agreements both expire in February 2026.

[2] (2) Unfunded commitments of $80.0 million reflects Senior Notes expected to be issued on or before March 14, 2023