Regulatory assets and liabilities (Tables)

12 Months Ended

Dec. 31, 2017

Regulatory Assets and Liabilities Disclosure [Abstract]

Regulatory assets

The following table summarizes the individual components of unamortized regulatory assets and liabilities as of December 31:

	Estimated Recovery Period	*	2017			2016
			(In thousands)
Regulatory assets:
Pension and postretirement benefits (a)	(e)		$	163,896		$	176,025
Taxes recoverable from customers (a)	Over plant lives		12,073			28,278
Manufactured gas plant sites remediation (a)	-		18,213			18,259
Asset retirement obligations (a)	Over plant lives		56,078			42,580
Natural gas costs recoverable through rate adjustments (b)	Up to 1 year		14,465			2,242
Long-term debt refinancing costs (a)	Up to 20 years		5,563			6,248
Costs related to identifying generation development (a)	Up to 9 years		2,960			3,407
Other (a) (b)	Up to 20 years		27,715			30,281
Total regulatory assets			300,963			307,320
Regulatory liabilities:
Plant removal and decommissioning costs (c)			176,190			176,972
Taxes refundable to customers (c)			279,668			11,010
Pension and postretirement benefits (c)			11,056			9,099
Natural gas costs refundable through rate adjustments (d)			28,514			25,580
Other (c) (d)			23,870			19,191
Total regulatory liabilities			519,298			241,852
Net regulatory position			$	(218,335	)	$	65,468

* Estimated recovery period for regulatory assets currently being recovered in rates charged to customers.

(a) Included in deferred charges and other assets - other on the Consolidated Balance Sheets.

(b) Included in prepayments and other current assets on the Consolidated Balance Sheets.

(c) Included in deferred credits and other liabilities - other on the Consolidated Balance Sheets.

(d) Included in other accrued liabilities on the Consolidated Balance Sheets.

(e) Recovered as expense is incurred or cash contributions are made.

Regulatory liabilities

The following table summarizes the individual components of unamortized regulatory assets and liabilities as of December 31:

	Estimated Recovery Period	*	2017			2016
			(In thousands)
Regulatory assets:
Pension and postretirement benefits (a)	(e)		$	163,896		$	176,025
Taxes recoverable from customers (a)	Over plant lives		12,073			28,278
Manufactured gas plant sites remediation (a)	-		18,213			18,259
Asset retirement obligations (a)	Over plant lives		56,078			42,580
Natural gas costs recoverable through rate adjustments (b)	Up to 1 year		14,465			2,242
Long-term debt refinancing costs (a)	Up to 20 years		5,563			6,248
Costs related to identifying generation development (a)	Up to 9 years		2,960			3,407
Other (a) (b)	Up to 20 years		27,715			30,281
Total regulatory assets			300,963			307,320
Regulatory liabilities:
Plant removal and decommissioning costs (c)			176,190			176,972
Taxes refundable to customers (c)			279,668			11,010
Pension and postretirement benefits (c)			11,056			9,099
Natural gas costs refundable through rate adjustments (d)			28,514			25,580
Other (c) (d)			23,870			19,191
Total regulatory liabilities			519,298			241,852
Net regulatory position			$	(218,335	)	$	65,468

* Estimated recovery period for regulatory assets currently being recovered in rates charged to customers.

(a) Included in deferred charges and other assets - other on the Consolidated Balance Sheets.

(b) Included in prepayments and other current assets on the Consolidated Balance Sheets.

(c) Included in deferred credits and other liabilities - other on the Consolidated Balance Sheets.

(d) Included in other accrued liabilities on the Consolidated Balance Sheets.

(e) Recovered as expense is incurred or cash contributions are made.