Long-Term Debt - Additional Information (Detail) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Document Period End Date		Jun. 30, 2023
Long-term debt including current maturities		$ 666,800	$ 600,800
Debt Instrument, Unused Borrowing Capacity, Amount		255,000
Short-term borrowing		$ 95,807	202,157
Uncollateralized Senior Note Due December Two Thousand Thirty Four [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		2.98%
Debt instrument, maturity date		Dec. 20, 2034
Term Note Due January Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		$ 70,000	70,000
3.48% note, due May 31, 2038 [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		50,000	50,000
3.25% note, due April 30, 2032 [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		63,000	66,500
Aggregated Unfunded Commitments [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		0
Equipment Security Note
Debt Instrument [Line Items]
Long-term debt including current maturities		$ 8,078	8,517
Debt Instrument, Interest Rate, Stated Percentage		2.46%
Debt instrument, maturity date		Sep. 24, 2031
Uncollateralized Senior Note Due March 15, 2042
Debt Instrument [Line Items]
Long-term debt including current maturities		$ 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]
Long-term debt including current maturities		$ 80,000
Debt Instrument, Interest Rate, Stated Percentage		5.43%
Debt instrument, maturity date		Mar. 14, 2038
Uncollateralized Senior Note Due January Two Thousand Thirty Seven
Debt Instrument [Line Items]
Long-term debt including current maturities		$ 50,000	$ 50,000
Debt Instrument, Interest Rate, Stated Percentage		2.49%
Debt instrument, maturity date		Jan. 25, 2037
Aggregate Shelf Agreements [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		$ 350,000
MetLife [Member]
Debt Instrument [Line Items]
Senior notes	[1]	200,000
Long-term debt including current maturities		50,000
Debt Instrument, Unused Borrowing Capacity, Amount	[1]	150,000
Prudential [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities	[1]	300,000
Debt Instrument, Unused Borrowing Capacity, Amount	[1]	105,000
Prudential [Member] | Aggregated Unfunded Commitments [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities	[1]	0
Prudential [Member] | Uncollateralized Senior Note Due March 14, 2038
Debt Instrument [Line Items]
Long-term debt including current maturities		80,000
Maximum [Member] | Aggregate Shelf Agreements [Member]
Debt Instrument [Line Items]
Senior notes		605,000
Maximum [Member] | Prudential [Member]
Debt Instrument [Line Items]
Senior notes	[1]	$ 405,000

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