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Debt (Details) - USD ($) $ in Thousands		9 Months Ended
Debt (Details) - USD ($) $ in Thousands	Jan. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Debt [Abstract]
Total long-term debt		$ 103,328		$ 95,908
Less discount on issuance of long-term debt		(195)		(204)
Less unamortized debt issuance costs		(2,421)		(2,346)
Less current maturities		(6,500)		(30)
Long-term portion		94,212		93,328
10.17% Series A Senior Notes and 9.60% Series B Senior Notes [Member]
Debt [Abstract]
Face value	$ 11,000
10.17% Senior Notes, Series A, due 2019 [Member]
Debt [Abstract]
Total long-term debt		$ 0		6,000
Interest rate		10.17%
Maturity date		Feb. 01, 2019
9.60% Senior Notes, Series B, due 2019 [Member]
Debt [Abstract]
Total long-term debt		$ 0		5,000
Interest rate		9.60%
Maturity date		Feb. 01, 2019
1.00% Pennvest Note, due 2019 [Member]
Debt [Abstract]
Total long-term debt		$ 0		30
Interest rate		1.00%
10.05% Senior Notes, Series C, due 2020 [Member]
Debt [Abstract]
Total long-term debt		$ 6,500		6,500
Interest rate		10.05%
8.43% Senior Notes, Series D, due 2022 [Member]
Debt [Abstract]
Total long-term debt		$ 7,500		7,500
Interest rate		8.43%
Variable Rate Pennsylvania Economic Development Financing Authority Exempt Facilities Revenue Refunding Bonds, Series 2008A, due 2029 [Member]
Debt [Abstract]
Total long-term debt		$ 12,000		12,000
4.75% York County Industrial Development Authority Revenue Bonds, Series 2006, due 2036 [Member]
Debt [Abstract]
Total long-term debt		$ 10,500		10,500
Interest rate		4.75%
4.50% Pennsylvania Economic Development Financing Authority Exempt Facilities Revenue Refunding Bonds, Series 2014, due 2038 [Member]
Debt [Abstract]
Total long-term debt		$ 14,870		14,870
Interest rate		4.50%
5.00% Monthly Senior Notes, Series 2010A, due 2040 [Member]
Debt [Abstract]
Total long-term debt		$ 15,000		15,000
Interest rate		5.00%
4.00% - 4.50% York County Industrial Development Authority Exempt Facilities Revenue Bonds, Series 2015, due 2029 - 2045 [Member]
Debt [Abstract]
Total long-term debt		$ 10,000		10,000
4.00% - 4.50% York County Industrial Development Authority Exempt Facilities Revenue Bonds, Series 2015, due 2029 - 2045 [Member] \| Minimum [Member]
Debt [Abstract]
Interest rate		4.00%
4.00% - 4.50% York County Industrial Development Authority Exempt Facilities Revenue Bonds, Series 2015, due 2029 - 2045 [Member] \| Maximum [Member]
Debt [Abstract]
Interest rate		4.50%
4.54% Senior Notes, due 2049 [Member]
Debt [Abstract]
Total long-term debt		$ 20,000		0
Face value	20,000
Interest rate		4.54%
Maturity date		Jan. 31, 2049
Proceeds from debt, net of issuance costs	$ 19,820
Committed Lines of Credit, due 2021 [Member]
Debt [Abstract]
Total long-term debt		$ 6,958		$ 8,508
First Line of Credit [Member]
Debt [Abstract]
Maturity date		May 31, 2021
Renewed line of credit			$ 13,000
Second Line of Credit [Member]
Debt [Abstract]
Maturity date		May 31, 2021
Renewed line of credit			11,000
Third Line of Credit [Member]
Debt [Abstract]
Maturity date		Jun. 30, 2021
Renewed line of credit			$ 7,500
Fourth Line of Credit [Member]
Debt [Abstract]
Maturity date		Sep. 30, 2020
Renewed line of credit		$ 10,000