Long-Term Debt - Outstanding Long-Term Debt (Detail) - USD ($)		Sep. 30, 2020		Dec. 31, 2019
Debt Instrument [Line Items]
Total long-term debt		$ (536,500,000)		$ (486,600,000)
Debt Instrument, Unused Borrowing Capacity, Amount		310,000,000
Total Long-term debt		535,571,000		485,768,000
Less: current maturities		(15,600,000)		(45,600,000)
Less: debt issuance costs		922,000		822,000
Total long-term debt, net of current maturities		519,971,000		440,168,000
NYL Unsecured Debt [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (40,000,000.0)
Debt Instrument, Interest Rate, Stated Percentage		2.96%
Aggregated Unfunded Commitments [Member]
Debt Instrument [Line Items]
Total long-term debt		$ 0
Prudential Unfunded Commitments [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (50,000,000.0)
Debt Instrument, Interest Rate, Stated Percentage	[1],[2]	3.00%
New York Life [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (140,000,000)
9.08% bond, due June 1, 2022 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (7,993,000)	[3]	(7,990,000)
Debt Instrument, Interest Rate, Stated Percentage		9.08%
5.50% note, due October 12, 2020 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (2,000,000)		(2,000,000)
Debt Instrument, Interest Rate, Stated Percentage		5.50%
5.93% note, due October 31, 2023 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (10,500,000)		(12,000,000)
Debt Instrument, Interest Rate, Stated Percentage		5.93%
5.68% note, due June 30, 2026 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (17,400,000)		(20,300,000)
Debt Instrument, Interest Rate, Stated Percentage		5.68%
6.43% note, due May 2, 2028 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (5,600,000)		(6,300,000)
Debt Instrument, Interest Rate, Stated Percentage		6.43%
3.73% note, due December 16, 2028 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (18,000,000)		(18,000,000)
Debt Instrument, Interest Rate, Stated Percentage		3.73%
3.88% note, due May 15, 2029 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (45,000,000)		(50,000,000)
Debt Instrument, Interest Rate, Stated Percentage		3.88%
3.25% note, due April 30, 2032 [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (70,000,000)		(70,000,000)
3.48% note, due May 31, 2038 [Member]
Debt Instrument [Line Items]
Total long-term debt		(50,000,000)		(50,000,000)
Uncollateralized Senior Note Due November Two Thousand Thirty Eight [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (50,000,000)		(50,000,000)
Debt Instrument, Interest Rate, Stated Percentage		3.58%
Uncollateralized Senior Note Due August Two Thousand Thirty Nine [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (100,000,000)		(100,000,000)
Debt Instrument, Interest Rate, Stated Percentage		3.98%
Term Note Due January Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (70,000,000)		(70,000,000)
Term Note Due February Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Total long-term debt		0		$ (30,000,000)
Uncollateralized Senior Note Due July Two Thousand Thirty Five
Debt Instrument [Line Items]
Total long-term debt		$ (50,000,000)
Debt Instrument, Interest Rate, Stated Percentage		3.00%
Uncollateralized Senior Note Due August Two Thousand Thirty Five
Debt Instrument [Line Items]
Total long-term debt		$ (40,000,000)
Debt Instrument, Interest Rate, Stated Percentage		2.96%
Aggregate Shelf Agreements [Member]
Debt Instrument [Line Items]
Total long-term debt		$ (360,000,000)
Aggregate Shelf Agreements [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		670,000,000
Prudential [Member]
Debt Instrument [Line Items]
Total long-term debt		(220,000,000)
Debt Instrument, Unused Borrowing Capacity, Amount	[1],[2]	150,000,000
Prudential [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	[1],[2]	370,000,000
MetLife [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	[4]	150,000,000.0
Debt Instrument, Unused Borrowing Capacity, Amount	[4]	$ 150,000,000

[1] 2) In April 2020, the Prudential Shelf Agreement was amended to increase the available borrowing capacity to $150.0 million. The Shelf Agreement expires in April 2023.

[2] (1) In January 2020, we requested and Prudential accepted our request to purchase $50.0 million of our unsecured debt. We issued the Shelf Notes in July 2020 at the rate of 3.00 percent per annum.

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

[4] (3) In May 2020, we reached into an agreement with MetLife to provide a new $150.0 million MetLife Shelf Agreement for a three-year term ending May 2023.