Long-Term Debt - Outstanding Long-Term Debt (Detail) - USD ($) $ in Thousands		Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Total long-term debt		$ (618,600)	$ (568,800)
Debt Instrument, Unused Borrowing Capacity, Amount		250,000
Total Long-term debt		617,595	567,865
Less: current maturities		(19,717)	(17,962)
Less: debt issuance costs		970	913
Total long-term debt, net of current maturities		597,878	549,903
Aggregated Unfunded Commitments [Member]
Debt Instrument [Line Items]
Total long-term debt		0
5.93% note, due October 31, 2023 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (6,000)	(6,000)
Debt Instrument, Interest Rate, Stated Percentage		5.93%
5.68% note, due June 30, 2026 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (14,500)	(14,500)
Debt Instrument, Interest Rate, Stated Percentage		5.68%
6.43% note, due May 2, 2028 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (4,900)	(4,900)
Debt Instrument, Interest Rate, Stated Percentage		6.43%
3.73% note, due December 16, 2028 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (14,000)	(14,000)
Debt Instrument, Interest Rate, Stated Percentage		3.73%
3.88% note, due May 15, 2029 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (40,000)	(40,000)
Debt Instrument, Interest Rate, Stated Percentage		3.88%
3.25% note, due April 30, 2032 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (70,000)	(70,000)
3.48% note, due May 31, 2038 [Member]
Debt Instrument [Line Items]
Total long-term debt		(50,000)	(50,000)
Uncollateralized Senior Note Due November Two Thousand Thirty Eight [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (50,000)	(50,000)
Debt Instrument, Interest Rate, Stated Percentage		3.58%
Uncollateralized Senior Note Due July Two Thousand Thirty Five
Debt Instrument [Line Items]
Total long-term debt		$ (50,000)	(50,000)
Debt Instrument, Interest Rate, Stated Percentage		3.00%
Uncollateralized Senior Note Due August Two Thousand Thirty Five
Debt Instrument [Line Items]
Total long-term debt		$ (40,000)	(40,000)
Debt Instrument, Interest Rate, Stated Percentage		2.96%
Uncollateralized Senior Note Due November Two Thousand Thirty Nine
Debt Instrument [Line Items]
Total long-term debt		$ (100,000)	(100,000)
Equipment Security Note
Debt Instrument [Line Items]
Total long-term debt		$ (9,165)	(9,378)
Debt Instrument, Interest Rate, Stated Percentage		2.46%
Equipment Security Note | Marlin Gas Services [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (9,600)
Uncollateralized Senior Note Due January Two Thousand Thirty Seven
Debt Instrument [Line Items]
Total long-term debt		$ (50,000)	$ (50,000)
Debt Instrument, Interest Rate, Stated Percentage		2.49%
Uncollateralized Senior Note Due March 15, 2042
Debt Instrument [Line Items]
Total long-term debt		$ (50,000)
Debt Instrument, Interest Rate, Stated Percentage		2.95%
Aggregate Shelf Agreements [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (270,000)
Aggregate Shelf Agreements [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		520,000
Prudential [Member]
Debt Instrument [Line Items]
Total long-term debt	[1]	(220,000)
Debt Instrument, Unused Borrowing Capacity, Amount	[1]	150,000
Prudential [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	[1]	370,000
MetLife [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	[1]	150,000
Total long-term debt	[1]	(50,000)
Debt Instrument, Unused Borrowing Capacity, Amount	[1]	100,000
MetLife [Member] | Uncollateralized Senior Note Due March 15, 2042
Debt Instrument [Line Items]
Total long-term debt		$ (50,000)

[1] (1) The Prudential and MetLife Shelf Agreements expire in April 2023 and May 2023, respectively.