Regulatory Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2011

Regulatory Assets and Liabilities Disclosure [Abstract]

Schedule of Regulatory Assets And Liabilities

We have specific orders to cover approximately 98% of our regulatory assets and 96% of our regulatory liabilities.

	Note Reference	Remaining Amortization Period	December 31,
			2011			2010
			(in thousands)
Pension	13	Undetermined	$	128,844		$	94,500
Postretirement benefits	13	Undetermined	6,434			9,104
Competitive transition charges		1 Year	1,380			7,359
Distribution infrastructure projects	16	6 Years	4,883			—
Environmental clean-up	18	Various	16,998			15,438
Supply costs		1 Year	11,168			8,491
Energy supply derivatives	6	1 Year	20,312			29,721
Income taxes	10	Plant Lives	124,967			71,374
Deferred financing costs		Various	15,413			16,882
Other	—	Various	27,305			29,465
Total regulatory assets			$	357,704		$	282,334
Removal cost	4	Various	$	251,262		$	237,831
Gas storage sales		28 Years	11,672			12,092
Supply costs		1 Year	18,214			15,065
DGGS interim rates (subject to refund)	16	1 Year	10,984			—
Environmental clean-up		1 Year	1,645		1,645	467
State & local taxes & fees		1 Year	2,528			805
Other		Various	2,866			2,046
Total regulatory liabilities			$	299,171		$	268,306