Long-Term Debt - Outstanding Long-Term Debt (Detail) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total long-term debt		$ 211,400	$ 145,900
Capital lease obligation		2,425	3,471
Total Long-term debt		213,384	149,053
Less: current maturities		(12,136)	(12,099)
Less: debt issuance costs		(446)	(291)
Total long-term debt, net of current maturities		201,248	136,954
9.08% bond, due June 1, 2022 [Member]
Debt Instrument [Line Items]
Total long-term debt	[1]	7,981	7,978
6.64% note, due October 31, 2017 [Member]
Debt Instrument [Line Items]
Total long-term debt		2,727	2,727
5.50% note, due October 12, 2020 [Member]
Debt Instrument [Line Items]
Total long-term debt		8,000	8,000
5.93% note, due October 31, 2023 [Member]
Debt Instrument [Line Items]
Total long-term debt		19,500	21,000
5.68% note, due June 30, 2026 [Member]
Debt Instrument [Line Items]
Total long-term debt		26,100	29,000
Uncollateralized Senior Notes Due On May Two Thousand Twenty Eight [Member]
Debt Instrument [Line Items]
Total long-term debt		7,000	7,000
Uncollateralized Senior Note Two Due on December Two Thousand Twenty Eight [Member]
Debt Instrument [Line Items]
Total long-term debt		20,000	20,000
Uncollateralized Senior Notes Due On Two Thousand Twenty Nine [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
Promissory note [Member]
Debt Instrument [Line Items]
Total long-term debt		$ 97	$ 168

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