Long-Term Debt - Outstanding Long-Term Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term Debt	$ 327,200	$ 205,200
Capital lease obligation	1,310	2,070
Less: debt issuance costs	(567)	(433)
Long-term Debt and Capital Lease Obligations	327,955	206,816
Less: current maturities	(11,935)	(9,421)
Total long-term debt, net of current maturities	316,020	197,395
9.08% bond, due June 1, 2022
Debt Instrument [Line Items]
Long-term Debt	$ 7,986	7,982
Debt Instrument, Interest Rate, Stated Percentage	9.08%
6.64% note, due October 31, 2017
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.64%
5.50% note, due October 12, 2020
Debt Instrument [Line Items]
Long-term Debt	$ 4,000	6,000
Debt Instrument, Interest Rate, Stated Percentage	5.50%
5.93% note, due October 31, 2023
Debt Instrument [Line Items]
Long-term Debt	$ 15,000	18,000
Debt Instrument, Interest Rate, Stated Percentage	5.93%
5.68% note, due June 30, 2026
Debt Instrument [Line Items]
Long-term Debt	$ 23,200	26,100
Debt Instrument, Interest Rate, Stated Percentage	5.68%
6.43% note, due May 2, 2028
Debt Instrument [Line Items]
Long-term Debt	$ 7,000	7,000
Debt Instrument, Interest Rate, Stated Percentage	6.43%
3.73% note, due December 16, 2028
Debt Instrument [Line Items]
Long-term Debt	$ 20,000	20,000
Debt Instrument, Interest Rate, Stated Percentage	3.73%
3.88% note, due May 15, 2029
Debt Instrument [Line Items]
Long-term Debt	$ 50,000	50,000
Debt Instrument, Interest Rate, Stated Percentage	3.88%
Uncollateralized Senior Note Due April Two Thousand Thirty Two [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 70,000	70,000
Uncollateralized Senior Note Due May Two Thousand Thirty Eight [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 50,000
Debt Instrument, Interest Rate, Stated Percentage	3.48%
Uncollateralized Senior Note Due November Two Thousand Thirty Eight [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 50,000
Debt Instrument, Interest Rate, Stated Percentage	3.58%
Term Note Due January Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 30,000
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	0.75%
Debt Instrument, Interest Rate, Stated Percentage	3.23%
Promissory note
Debt Instrument [Line Items]
Long-term Debt	$ 26	$ 97

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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