Long-Term Debt - Outstanding Long-Term Debt (Detail) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Total long-term debt		$ (666,800)	$ (600,800)
Debt Instrument, Unused Borrowing Capacity, Amount		255,000
Total Long-term debt		665,736	599,871
Less: current maturities		(19,994)	(21,483)
Less: debt issuance costs		1,042	946
Total long-term debt, net of current maturities		645,742	578,388
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		$ (1,500)	(3,000)
Debt Instrument, Interest Rate, Stated Percentage		5.93%
Debt instrument, maturity date		Oct. 31, 2023
5.68% note, due June 30, 2026 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (8,700)	(11,600)
Debt Instrument, Interest Rate, Stated Percentage		5.68%
Debt instrument, maturity date		Jun. 30, 2026
6.43% note, due May 2, 2028 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (3,500)	(4,200)
Debt Instrument, Interest Rate, Stated Percentage		6.43%
Debt instrument, maturity date		May 02, 2028
3.73% note, due December 16, 2028 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (12,000)	(12,000)
Debt Instrument, Interest Rate, Stated Percentage		3.73%
Debt instrument, maturity date		Dec. 16, 2028
3.88% note, due May 15, 2029 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (30,000)	(35,000)
Debt Instrument, Interest Rate, Stated Percentage		3.88%
Debt instrument, maturity date		May 15, 2029
3.25% note, due April 30, 2032 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (63,000)	(66,500)
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%
Debt instrument, maturity date		Nov. 30, 2038
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%
Debt instrument, maturity date		Jul. 15, 2035
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%
Debt instrument, maturity date		Aug. 15, 2035
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		$ (8,078)	(8,517)
Debt Instrument, Interest Rate, Stated Percentage		2.46%
Debt instrument, maturity date		Sep. 24, 2031
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%
Debt instrument, maturity date		Jan. 25, 2037
Uncollateralized Senior Note Due March 15, 2042
Debt Instrument [Line Items]
Total long-term debt		$ (50,000)	$ (50,000)
Debt Instrument, Interest Rate, Stated Percentage		2.95%
Debt instrument, maturity date		Mar. 15, 2042
Uncollateralized Senior Note Due March 14, 2038
Debt Instrument [Line Items]
Total long-term debt		$ (80,000)
Debt Instrument, Interest Rate, Stated Percentage		5.43%
Debt instrument, maturity date		Mar. 14, 2038
Aggregate Shelf Agreements [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (350,000)
Aggregate Shelf Agreements [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		605,000
Prudential [Member]
Debt Instrument [Line Items]
Total long-term debt	[1]	(300,000)
Debt Instrument, Unused Borrowing Capacity, Amount	[1]	105,000
Prudential [Member] | Aggregated Unfunded Commitments [Member]
Debt Instrument [Line Items]
Total long-term debt	[1]	0
Prudential [Member] | Uncollateralized Senior Note Due March 14, 2038
Debt Instrument [Line Items]
Total long-term debt		(80,000)
Prudential [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	[1]	405,000
MetLife [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	[1]	200,000
Total long-term debt		(50,000)
Debt Instrument, Unused Borrowing Capacity, Amount	[1]	$ 150,000

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