Income Taxes - Schedule of Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Current Income Tax Expense
Federal	$ 4,882		$ 3,483		$ 0
State	2,382		1,990		742
Investment tax credit adjustments, net	(39)		(58)		(73)
Total current income tax expense	7,225		5,415		669
Deferred Income Tax Expense (1)
Total deferred income tax expense	14,860		13,881		17,320
Total Income Tax Expense	22,085		19,296		17,989
Property, plant and equipment
Deferred Income Tax Expense (1)
Total deferred income tax expense	16,758	[1]	13,688	[1]	16,670	[1]
Deferred gas costs
Deferred Income Tax Expense (1)
Total deferred income tax expense	(209)	[1]	515	[1]	591	[1]
Pensions and other employee benefits
Deferred Income Tax Expense (1)
Total deferred income tax expense	(335)	[1]	553	[1]	786	[1]
FPU merger related premium cost and deferred gain
Deferred Income Tax Expense (1)
Total deferred income tax expense	(686)	[1]	(509)	[1]	0
Net operating loss carryforwards
Deferred Income Tax Expense (1)
Total deferred income tax expense	62	[1]	740	[1]	(1,000)	[1]
Other
Deferred Income Tax Expense (1)
Total deferred income tax expense	$ (730)		$ (1,106)	[1]	$ 273	[1]

[1] As of December 31, 2013 2012(in thousands) Deferred Income Taxes Deferred income tax liabilities: Property, plant and equipment$134,414 $118,212Acquisition adjustment16,790 17,440Loss on reacquired debt573 572Deferred gas costs607 816Other2,850 2,784Total deferred income tax liabilities155,234 139,824Deferred income tax assets: Pension and other employee benefits5,390 7,382Environmental costs2,083 1,917Net operating loss carryforwards1,444 1,587Self insurance403 484Storm reserve liability1,109 1,058Other3,904 2,982Total deferred income tax assets14,333 15,410Deferred Income Taxes Per Consolidated Balance Sheet$140,901 $124,414