CONSOLIDATED STATEMENTS OF CHANGES IN COMMON SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	GSWC	Common Stock [Member]	Common Stock [Member] GSWC	Earnings Reinvested in the Business	Earnings Reinvested in the Business GSWC
Balances at Dec. 31, 2013	$ 492,404	$ 437,613	$ 253,961	$ 233,721	$ 238,443	$ 203,892
Balances (in shares) at Dec. 31, 2013			38,721,000	146
Balances (in shares) at Dec. 31, 2014			38,287,000	146
Add:
Net Income	61,058	47,857			61,058	47,857
Issuance of Common Shares	$ 589		$ 589
Issuance of Common Shares (in shares)	74,145		111,000
Exercise of stock options (in shares)	37,006
Tax benefit from employee stock-based awards	$ 533	514	$ 533	$ 514
Compensation on stock-based awards	1,508	1,206	1,508	1,206
Dividend equivalent rights on stock-based awards not paid in cash	197	166	$ 197	166
Stock Repurchased During Period, Shares			545,000
Stock Repurchased During Period, Value	17,180		$ 3,589		13,591
Deduct:
Dividends on Common Shares	32,111	52,000			32,111	52,000
Dividend equivalent rights on stock-based awards	197	166			197	166
Balances at Dec. 31, 2014	506,801	435,190	$ 253,199	$ 235,607	253,602	199,583
Balances (in shares) at Dec. 31, 2015			36,502,000	146
Add:
Net Income	$ 60,484	47,591			60,484	47,591
Issuance of Common Shares		872		$ 872
Issuance of Common Shares (in shares)	53,612
Exercise of stock options (in shares)	66,458
Exercise of stock options and other issuance of Common Shares	$ 1,198		$ 1,198
Exercise of stock options and other issuance of Common Shares (in shares)			120,000
Tax benefit from employee stock-based awards	877		$ 877
Compensation on stock-based awards	2,168	2,077	2,168	2,077
Dividend equivalent rights on stock-based awards not paid in cash	270	239	$ 270	239
Stock Repurchased During Period, Shares			1,905,000
Stock Repurchased During Period, Value	72,893		$ 12,690		60,203
Deduct:
Dividends on Common Shares	32,690	62,000			32,690	62,000
Dividend equivalent rights on stock-based awards	270	239			270	239
Balances at Dec. 31, 2015	465,945	423,730	$ 245,022	$ 238,795	220,923	184,935
Balances (in shares) at Dec. 31, 2016			36,571,000	146
Add:
Net Income	$ 59,743	46,969			59,743	46,969
Issuance of Common Shares (in shares)	56,900
Exercise of stock options (in shares)	12,546
Exercise of stock options and other issuance of Common Shares	$ 235		$ 235
Exercise of stock options and other issuance of Common Shares (in shares)			69,000
Tax benefit from employee stock-based awards	581	501	$ 581	$ 501
Compensation on stock-based awards	1,201	1,020	1,201	1,020
Dividend equivalent rights on stock-based awards not paid in cash	193	166	193	166
Deduct:
Dividends on Common Shares	33,408	25,450			33,408	25,450
Dividend equivalent rights on stock-based awards	193	166			193	166
Balances at Dec. 31, 2016	$ 494,297	$ 446,770	$ 247,232	$ 240,482	$ 247,065	$ 206,288