Long-Term Debt - Outstanding Long-Term Debt (Detail) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total long-term debt		$ (352,100)	$ (327,200)
Debt Instrument, Unused Borrowing Capacity, Amount		250,000
Finance lease obligation		0	1,310
Total Long-term debt		351,524	327,955
Less: current maturities		(75,600)	(11,935)
Less: debt issuance costs		564	567
Total long-term debt, net of current maturities		275,924	316,020
Aggregated Unfunded Commitments [Member]
Debt Instrument [Line Items]
Total long-term debt		(100,000)
Prudential Unfunded Commitments [Member]
Debt Instrument [Line Items]
Total long-term debt		(100,000)
New York Life [Member]
Debt Instrument [Line Items]
Total long-term debt		(100,000)
9.08% bond, due June 1, 2022 [Member]
Debt Instrument [Line Items]
Total long-term debt	[1]	(7,988)	(7,986)
5.50% note, due October 12, 2020 [Member]
Debt Instrument [Line Items]
Total long-term debt		(4,000)	(4,000)
5.93% note, due October 31, 2023 [Member]
Debt Instrument [Line Items]
Total long-term debt		(13,500)	(15,000)
5.68% note, due June 30, 2026 [Member]
Debt Instrument [Line Items]
Total long-term debt		(20,300)	(23,200)
6.43% note, due May 2, 2028 [Member]
Debt Instrument [Line Items]
Total long-term debt		(6,300)	(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)	(50,000)
Uncollateralized Senior Note Due November Two Thousand Thirty Eight [Member]
Debt Instrument [Line Items]
Total long-term debt		(50,000)	(50,000)
Term Note Due January Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Total long-term debt		(30,000)	(30,000)
Term Note Due February Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Total long-term debt		(30,000)
Promissory note [Member]
Debt Instrument [Line Items]
Total long-term debt		0	$ (26)
Aggregate Shelf Agreements [Member]
Debt Instrument [Line Items]
Total long-term debt		(170,000)
Aggregate Shelf Agreements [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		520,000
Prudential [Member]
Debt Instrument [Line Items]
Total long-term debt		(70,000)
Debt Instrument, Unused Borrowing Capacity, Amount		50,000
Prudential [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		220,000
MetLife [Member]
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount		150,000
MetLife [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		150,000
New York Life [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		100,000
Debt Instrument, Unused Borrowing Capacity, Amount		50,000
New York Life [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 150,000

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