Regulation and Rates (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 01, 2015	May. 01, 2015	Jan. 01, 2015	Dec. 31, 2014	Dec. 01, 2014	Nov. 01, 2014	May. 23, 2014	May. 01, 2014	Jul. 02, 2013	Jun. 25, 2013
Regulatory Assets [Line Items]
Net Income (Loss) Attributable to Parent	$ 25,616	$ 41,113	$ 141,292	$ 148,705
Subsidiaries [Member]
Regulatory Assets [Line Items]
Net Income (Loss) Attributable to Parent	42,699	$ 57,834	171,799	$ 178,916
Rate Case, Approved Effective Weighted Cost of Capital													7.77%
Rate Case, Approved Effective Common Equity in Capital Structure													48.00%
Rate Case, Approved Effective Return on Equity													9.80%
Decoupling Mechanism [Member] | Natural Gas [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Percentage Increase (Decrease)							2.20%
Decoupling Mechanism [Member] | Subsidiaries [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Increase (Decrease)						$ (12,000)
Decoupling Mechanism [Member] | Subsidiaries [Member] | Electric [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Increase (Decrease)						$ 53,800						$ 10,600
Public Utilities, Rate Case, Approved Effective Annual Rate Percentage Increase (Decrease)						2.60%						0.50%
Decoupling Mechanism [Member] | Subsidiaries [Member] | Natural Gas [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Increase (Decrease)						$ 22,000		$ (1,300)				$ (1,000)
Public Utilities, Rate Case, Approved Effective Annual Rate Percentage Increase (Decrease)						2.10%						(0.10%)
Power Cost Only Rate Case (PCORC) [Member] | Subsidiaries [Member] | Electric [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Increase (Decrease)									$ (19,400)		$ (9,600)
Public Utilities, Rate Case, Approved Effective Annual Rate Percentage Increase (Decrease)									(0.90%)		(0.50%)
Purchased Gas Adjustment (PGA) [Member] | Subsidiaries [Member] | Natural Gas [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Increase (Decrease)										$ 23,300
Public Utilities, Rate Case, Approved Effective Annual Rate Percentage Increase (Decrease)										2.50%
Property tax tracker [Member] [Domain] [Domain] | Subsidiaries [Member] | Electric [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Increase (Decrease)						$ 6,500	$ 0					$ 11,000
Public Utilities, Rate Case, Approved Effective Annual Rate Percentage Increase (Decrease)						0.30%
Property tax tracker [Member] [Domain] [Domain] | Subsidiaries [Member] | Natural Gas [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Increase (Decrease)					$ (2,300)							$ 5,600
Public Utilities, Rate Case, Approved Effective Annual Rate Percentage Increase (Decrease)					(0.20%)							0.60%
Conservation Rider [Member] | Subsidiaries [Member] | Electric [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Increase (Decrease)												$ 12,200
Public Utilities, Rate Case, Approved Effective Annual Rate Percentage Increase (Decrease)												0.60%
Conservation Rider [Member] | Subsidiaries [Member] | Natural Gas [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Increase (Decrease)												$ 300
Maximum [Member] | Decoupling Mechanism [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Percentage Increase (Decrease)							3.00%
Deferred Revenue [Domain] | Decoupling Mechanism [Member] | Subsidiaries [Member] | Electric [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Increase (Decrease)								1,900
Deferred Revenue [Domain] | Decoupling Mechanism [Member] | Subsidiaries [Member] | Natural Gas [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Increase (Decrease)								$ 8,200
Range 1 [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Amount	17,000		17,000
Range 2 [Member] [Member] | Minimum [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Amount	17,000		17,000
Range 2 [Member] [Member] | Maximum [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Amount	40,000		40,000
Range 3 [Member] [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Amount	$ 40,000		$ 40,000
Over Recovery [Member] | Range 1 [Member] | Customers share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	0.00%		0.00%
Over Recovery [Member] | Range 1 [Member] | Company's share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	100.00%		100.00%
Over Recovery [Member] | Range 2 [Member] [Member] | Customers share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	65.00%		65.00%
Over Recovery [Member] | Range 2 [Member] [Member] | Company's share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	35.00%		35.00%
Over Recovery [Member] | Range 3 [Member] [Member] | Customers share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	90.00%		90.00%
Over Recovery [Member] | Range 3 [Member] [Member] | Company's share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	10.00%		10.00%
Under Recovery [Member] | Range 1 [Member] | Customers share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	0.00%		0.00%
Under Recovery [Member] | Range 1 [Member] | Company's share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	100.00%		100.00%
Under Recovery [Member] | Range 2 [Member] [Member] | Customers share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	50.00%		50.00%
Under Recovery [Member] | Range 2 [Member] [Member] | Company's share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	50.00%		50.00%
Under Recovery [Member] | Range 3 [Member] [Member] | Customers share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	90.00%		90.00%
Under Recovery [Member] | Range 3 [Member] [Member] | Company's share [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Percentage	10.00%		10.00%
Deferral Trigger [Member] [Member]
Regulatory Assets [Line Items]
Annual Power Cost Variability, Amount	$ 20,000		$ 20,000											$ 30,000