Long-Term Debt - Outstanding Long-Term Debt (Detail) - USD ($) $ in Thousands		Mar. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Total long-term debt		$ (678,800)	$ (600,800)
Debt Instrument, Unused Borrowing Capacity, Amount		255,000
Total Long-term debt		677,773	599,871
Less: current maturities		(21,489)	(21,483)
Less: debt issuance costs		1,075	946
Total long-term debt, net of current maturities		656,284	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		$ (3,000)	(3,000)
Debt Instrument, Interest Rate, Stated Percentage		5.93%
5.68% note, due June 30, 2026 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (11,600)	(11,600)
Debt Instrument, Interest Rate, Stated Percentage		5.68%
6.43% note, due May 2, 2028 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (4,200)	(4,200)
Debt Instrument, Interest Rate, Stated Percentage		6.43%
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%
3.88% note, due May 15, 2029 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (35,000)	(35,000)
Debt Instrument, Interest Rate, Stated Percentage		3.88%
3.25% note, due April 30, 2032 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (64,750)	(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%
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		$ (8,298)	(8,517)
Debt Instrument, Interest Rate, Stated Percentage		2.46%
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)	$ (50,000)
Debt Instrument, Interest Rate, Stated Percentage		2.95%
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%
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
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 both expire in February 2026.