Regulatory assets and liabilities (Tables)

12 Months Ended

Dec. 31, 2012

Regulatory Assets and Liabilities Disclosure [Abstract]

Regulatory assets and liabilities

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

	Estimated Recovery Period	*	2012			2011
			(In thousands)
Regulatory assets:
Pension and postretirement benefits (a)	(e)		$	166,477		$	171,492
Deferred income taxes	**		121,781			119,189
Manufactured gas plant sites remediation (a)	Up to 5 years		15,828			8,150
Plant costs (a)	Over plant lives		10,348			10,256
Long-term debt refinancing costs (a)	Up to 25 years		9,144			10,112
Taxes recoverable from customers (a)	—		9,078			12,433
Costs related to identifying generation development (a)	Up to 14 years		5,773			9,817
Other (a) (b)	Largely within 1 year		12,765			17,560
Total regulatory assets			351,194			359,009
Regulatory liabilities:
Plant removal and decommissioning costs (c)			296,037			289,972
Deferred income taxes**			82,077			84,963
Natural gas costs refundable through rate adjustments (d)			35,328			45,064
Taxes refundable to customers (c)			24,212			31,837
Other (c) (d)			12,828			8,393
Total regulatory liabilities			450,482			460,229
Net regulatory position			$	(99,288	)	$	(101,220	)

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

** Represents deferred income taxes related to regulatory assets and liabilities. The deferred income tax assets are not earning a rate of return.

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

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

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

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

(e) Recovered as expense is incurred.