Long-Term Debt - Outstanding Long-Term Debt (Detail) - USD ($) $ in Thousands		Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total long-term debt		$ 250,700		$ 205,200
Capital lease obligation		987		2,070
Total Long-term debt		251,210		206,816
Less: current maturities		(9,613)		(9,421)
Less: debt issuance costs		(488)		(433)
Total long-term debt, net of current maturities		241,597		197,395
9.08% bond, due June 1, 2022 [Member]
Debt Instrument [Line Items]
Total long-term debt	[1]	7,985		7,982
5.50% note, due October 12, 2020 [Member]
Debt Instrument [Line Items]
Total long-term debt		6,000		6,000
5.93% note, due October 31, 2023 [Member]
Debt Instrument [Line Items]
Total long-term debt		16,500		18,000
5.68% note, due June 30, 2026 [Member]
Debt Instrument [Line Items]
Total long-term debt		23,200		26,100
6.43% note, due May 2, 2028 [Member]
Debt Instrument [Line Items]
Total long-term debt		7,000		7,000
3.73% note, due December 16, 2028 [Member]
Debt Instrument [Line Items]
Total long-term debt		20,000		20,000
3.88% note, due May 15, 2029 [Member]
Debt Instrument [Line Items]
Total long-term debt		50,000		50,000
3.25% note, due April 30, 2032 [Member]
Debt Instrument [Line Items]
Total long-term debt		70,000		70,000
3.48% note, due May 31, 2038 [Member]
Debt Instrument [Line Items]
Total long-term debt		50,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Total long-term debt			$ 25,000
Promissory note [Member]
Debt Instrument [Line Items]
Total long-term debt		$ 26		$ 97

[1] FPU secured first mortgage bonds are guaranteed by Chesapeake Utilities.