Leases - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2019 USD ($)
Operating Leased Assets [Line Items]
Finance leases	$ 0
Operating lease, description	TEC has operating leases for buildings, land, telecommunication services and rail cars.
Operating lease, existence of option to extend	true
Operating lease options to extend	options to extend the leases for up to an additional 65 years
Operating lease expense	$ 1,000,000
Option to purchase assets related to CNG stations	Customers have the option to purchase the assets related to the CNG stations at any time after 2021 by paying a make-whole payment at the date of the purchase based on a targeted internal rate of return
Maximum [Member]
Operating Leased Assets [Line Items]
Operating lease term of contract	12 months
Operating lease renewal term	67 years
Minimum [Member]
Operating Leased Assets [Line Items]
Operating lease renewal term	2 years