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Employee Benefit Plans (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Employee benefit plans
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 755		$ 568	$ 394
Estimated future benefit payments
Increase (Decrease) in Pension and Postretirement Obligations	$ 616		(2,356)	4,396
Healthcare Cost Trend Rate
Initial health care cost for employees under age of 65 (as a percent)	6.30%
Ultimate health care cost for employees under age of 65 (as a percent)	4.60%
Initial Health care cost for employees of age 65 and over (as a percent)	6.70%
Ultimate health care cost for employees of age 65 and over (as a percent)	4.50%
Effects of one-percentage-point change in assumed health care cost trend rates
Effect on total of service and interest cost components -1 Percentage Point Increase	$ 78
Effect on total of service and interest cost components -1 Percentage Point Decrease	(66)
Effect on post-retirement benefit obligation -1 Percentage Point Increase	1,021
Effect on post-retirement benefit obligation -1 Percentage Point Decrease	(879)
Defined contribution plan
Employer's contribution	$ 2,100		1,900	1,900
Fixed income securities | Maximum
Employer's contribution and fair value of plan assets
Maturity period of investments	20 years
Fixed income securities | Minimum
Employer's contribution and fair value of plan assets
Maturity period of investments	1 year
GSWC
Estimated future benefit payments
Increase (Decrease) in Pension and Postretirement Obligations	$ 616		(2,356)	4,396
Pension Benefits
Regulatory Adjustment:
Amount of under-collection included in the two-way pension balancing account	$ (523)		$ (1,622)	1,920
Actual and Target Asset Allocations
Actual Asset Allocations, Total (as a percent)	100.00%		100.00%
Target Asset Allocation for 2013, Total (as a percent)	100.00%
Employer's contribution and fair value of plan assets
Total investments measured at fair value	$ 142,174		$ 140,561	$ 127,534
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0
Employer contributions	6,739		$ 8,209
Expected employer's contribution in 2013	5,500
Estimated future benefit payments
2014	5,857
2015	6,381
2016	6,865
2017	7,393
2018	7,980
Thereafter	48,469
Total	$ 82,945
Expected long-term return on plan assets (as a percentage)	7.00%		7.00%	7.00%
Pension Benefits | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			$ 140,561
Pension Benefits | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value			$ 140,561
Pension Benefits | Cash equivalents
Actual and Target Asset Allocations
Actual Asset Allocations, Total (as a percent)	0.00%		0.00%
Employer's contribution and fair value of plan assets
Total investments measured at fair value	$ 469
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0
Pension Benefits | Cash equivalents | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			$ 497
Pension Benefits | Cash equivalents | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | Cash equivalents | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | Cash equivalents | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value			497
Pension Benefits | Fixed income securities
Employer's contribution and fair value of plan assets
Total investments measured at fair value	56,218
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0
Pension Benefits | Fixed income securities | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			54,865
Pension Benefits | Fixed income securities | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | Fixed income securities | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | Fixed income securities | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value			$ 54,865
Pension Benefits | Equity securities
Actual and Target Asset Allocations
Actual Asset Allocations, Total (as a percent)	55.00%		61.00%
Target Asset Allocation for 2013, Total (as a percent)	60.00%
Pension Benefits | Equity securities | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			$ 85,199
Pension Benefits | Equity securities | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | Equity securities | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | Equity securities | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value			85,199
Pension Benefits | U.S. small cap stocks
Employer's contribution and fair value of plan assets
Total investments measured at fair value	$ 21,219
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0
Pension Benefits | U.S. small cap stocks | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			22,325
Pension Benefits | U.S. small cap stocks | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | U.S. small cap stocks | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | U.S. small cap stocks | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value			22,325
Pension Benefits | U.S. large cap stocks
Employer's contribution and fair value of plan assets
Total investments measured at fair value	42,395
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0
Pension Benefits | U.S. large cap stocks | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			42,886
Pension Benefits | U.S. large cap stocks | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | U.S. large cap stocks | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | U.S. large cap stocks | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value			42,886
Pension Benefits | International funds
Employer's contribution and fair value of plan assets
Total investments measured at fair value	14,455
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0
Pension Benefits | International funds | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			11,318
Pension Benefits | International funds | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | International funds | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | International funds | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value			$ 11,318
Pension Benefits | Equity Funds [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	78,069
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0
Pension Benefits | Real Estate Funds [Member]
Actual and Target Asset Allocations
Actual Asset Allocations, Total (as a percent)	5.00%		0.00%
Employer's contribution and fair value of plan assets
Total investments measured at fair value	$ 7,418
Pension Benefits | Real estate funds
Employer's contribution and fair value of plan assets
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0
Pension Benefits | Real estate funds | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			$ 8,670
Pension Benefits | Real estate funds | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | Real estate funds | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value			0
Pension Benefits | Real estate funds | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value			$ 8,670
Pension Benefits | Debt securities
Actual and Target Asset Allocations
Actual Asset Allocations, Total (as a percent)	40.00%		39.00%
Target Asset Allocation for 2013, Total (as a percent)	40.00%
Pension Benefits | GSWC
Regulatory Adjustment:
Amount of under-collection included in the two-way pension balancing account	$ (523)		$ (1,600)	$ (1,900)
Post-Retirement Medical Plans
Regulatory Adjustment:
Amount of under-collection included in the two-way pension balancing account	$ 0		$ 0	0
Actual and Target Asset Allocations
Actual Asset Allocations, Total (as a percent)	100.00%		100.00%
Target Asset Allocation for 2013, Total (as a percent)	100.00%
Employer's contribution and fair value of plan assets
Total investments measured at fair value	$ 10,614		$ 10,723	$ 9,873
Employer contributions	109		241
Estimated future benefit payments
2014	535
2015	568
2016	626
2017	676
2018	722
Thereafter	4,318
Total	7,445
Post-Retirement Medical Plans | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	10,614		10,723
Post-Retirement Medical Plans | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
Post-Retirement Medical Plans | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
Post-Retirement Medical Plans | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value	$ 10,614		$ 10,723
Post-Retirement Medical Plans | Cash equivalents
Actual and Target Asset Allocations
Actual Asset Allocations, Total (as a percent)	2.00%		2.00%
Post-Retirement Medical Plans | Cash equivalents | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	$ 31		$ 185
Post-Retirement Medical Plans | Cash equivalents | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
Post-Retirement Medical Plans | Cash equivalents | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
Post-Retirement Medical Plans | Cash equivalents | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value	31		185
Post-Retirement Medical Plans | Fixed income securities | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	4,182		4,105
Post-Retirement Medical Plans | Fixed income securities | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
Post-Retirement Medical Plans | Fixed income securities | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
Post-Retirement Medical Plans | Fixed income securities | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value	$ 4,182		$ 4,105
Post-Retirement Medical Plans | Equity securities
Actual and Target Asset Allocations
Actual Asset Allocations, Total (as a percent)	60.00%		60.00%
Target Asset Allocation for 2013, Total (as a percent)	60.00%
Post-Retirement Medical Plans | U.S. large cap stocks | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	$ 6,401		$ 6,433
Post-Retirement Medical Plans | U.S. large cap stocks | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
Post-Retirement Medical Plans | U.S. large cap stocks | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
Post-Retirement Medical Plans | U.S. large cap stocks | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value	$ 6,401		$ 6,433
Post-Retirement Medical Plans | Real Estate Funds [Member]
Actual and Target Asset Allocations
Actual Asset Allocations, Total (as a percent)	0.00%		0.00%
Post-Retirement Medical Plans | Debt securities
Actual and Target Asset Allocations
Actual Asset Allocations, Total (as a percent)	38.00%		38.00%
Target Asset Allocation for 2013, Total (as a percent)	40.00%
Union plan
Estimated future benefit payments
Expected long-term return on plan assets (as a percentage)	7.00%	[1]	7.00%	7.00%
Non-union plan
Estimated future benefit payments
Expected long-term return on plan assets (as a percentage)	4.20%	[1]	4.20%	4.20%
SERP
Employer's contribution and fair value of plan assets
Total investments measured at fair value	$ 0		$ 0
Estimated future benefit payments
2014	411
2015	484
2016	635
2017	693
2018	1,093
Thereafter	5,567
Total	8,883
Balance in Rabbi Trust
Balance in Rabbi Trust	9,900
SERP | Rabbi Trust | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	9,866		8,765
SERP | Rabbi Trust | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
SERP | Rabbi Trust | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
SERP | Rabbi Trust | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value	9,866		8,765
SERP | Rabbi Trust | Cash equivalents | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	39		29
SERP | Rabbi Trust | Cash equivalents | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
SERP | Rabbi Trust | Cash equivalents | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
SERP | Rabbi Trust | Cash equivalents | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value	39		29
SERP | Rabbi Trust | Fixed income securities | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	3,903		3,454
SERP | Rabbi Trust | Fixed income securities | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
SERP | Rabbi Trust | Fixed income securities | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
SERP | Rabbi Trust | Fixed income securities | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value	3,903		3,454
SERP | Rabbi Trust | Equity securities | Fair Value, Inputs, Level 1 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	5,924		5,282
SERP | Rabbi Trust | Equity securities | Level 2
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
SERP | Rabbi Trust | Equity securities | Fair Value, Inputs, Level 3 [Member]
Employer's contribution and fair value of plan assets
Total investments measured at fair value	0		0
SERP | Rabbi Trust | Equity securities | Total
Employer's contribution and fair value of plan assets
Total investments measured at fair value	5,924		$ 5,282
Pension Costs and Other Postretirement Benefit Costs [Member] | GSWC
Regulatory Adjustment:
Regulatory asset authorized under settlement	19,800
Pension Costs and Other Postretirement Benefit Costs [Member] | Two-way pension balancing account | GSWC
Regulatory Adjustment:
Regulatory asset authorized under settlement	$ 2,200
[1] *7.0% for union plan, 4.2% for non-union, net of income taxes in 2015, 2014 and 2013.

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Represents the initial health care cost for employees of age sixty-five and over.

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The ultimate trend rate for health care costs for employees of age sixty-five and over.

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An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

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The increase in the fair value of plan assets from contributions made by the employer.

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The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

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The effect of a one-percentage-point increase in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

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Amount of benefits from a defined benefit plan expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the remainder of the fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Target allocation of investments of this type to total plan assets presented on a weighted average basis.

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The amount of the cost recognized during the period for defined contribution plans.

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