Long-Term Debt - Outstanding Long-Term Debt (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	May 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Long-term Debt	$ 122,000		$ 110,100
Capital lease obligation	6,978	7,100
Long-term Debt and Capital Lease Obligations	128,945		110,103
Less: current maturities	(11,353)		(8,196)
Total long-term debt, net of current maturities	117,592		101,907
9.57% bond, due May 1, 2018
Debt Instrument [Line Items]
Long-term Debt	0		5,444
10.03% bond, due May 1, 2018
Debt Instrument [Line Items]
Long-term Debt	0		2,994
9.08% bond, due June 1, 2022
Debt Instrument [Line Items]
Long-term Debt	7,967		7,962
7.83% note, due January 1, 2015
Debt Instrument [Line Items]
Long-term Debt	2,000		4,000
6.64% note, due October 31, 2017
Debt Instrument [Line Items]
Long-term Debt	10,909		13,636
5.50% note, due October 12, 2020
Debt Instrument [Line Items]
Long-term Debt	14,000		16,000
5.93% note, due October 31, 2023
Debt Instrument [Line Items]
Long-term Debt	30,000		30,000
5.68% note, due June 30, 2026
Debt Instrument [Line Items]
Long-term Debt	29,000		29,000
6.43% note, due May 2, 2028
Debt Instrument [Line Items]
Long-term Debt	7,000
3.73% note, due December 16, 2028
Debt Instrument [Line Items]
Long-term Debt	20,000
8.25% due March 1, 2014
Debt Instrument [Line Items]
Long-term Debt	646		942
Promissory note
Debt Instrument [Line Items]
Long-term Debt	$ 445		$ 125