Pension and Other Post-Retirement Benefits In Text Linking (Details) (USD $)	8 Months Ended	12 Months Ended											12 Months Ended
	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Pension Plans, Defined Benefit [Member] Rate	Dec. 31, 2011 Pension Plans, Defined Benefit [Member] Rate	Dec. 31, 2010 Pension Plans, Defined Benefit [Member] Rate	Dec. 31, 2012 BSWC Pension Plans, Defined Benefit [Member] Rate	Dec. 31, 2012 Other Postretirement Benefit Plans, Defined Benefit [Member] Rate	Dec. 31, 2011 Other Postretirement Benefit Plans, Defined Benefit [Member] Rate	Dec. 31, 2010 Other Postretirement Benefit Plans, Defined Benefit [Member] Rate	Dec. 31, 2012 Barnstable Water PBOP [Member]	Dec. 31, 2011 Barnstable Water PBOP [Member]	Dec. 31, 2012 Supplemental Executive Retirement Plan [Member]	Dec. 31, 2011 Supplemental Executive Retirement Plan [Member]	Dec. 31, 2010 Supplemental Executive Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost				$ 3,724,000	$ 1,959,000	$ 2,009,000	$ 4,000
Defined Benefit Plan, Accumulated Benefit Obligation				56,967,000	41,855,000
Defined Benefit Plan, Expected Return on Plan Assets		0		2,693,000	2,456,000	2,507,000		269,000	267,000	306,000
Defined Benefit Plan, Contributions by Employer				585,000	1,200,000			22,000	235,000
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year				2,490,000				850,000
Defined Benefit Plan, Benefit Obligation				66,501,000	49,102,000	40,758,000	4,076,000	13,322,000	12,842,000	13,443,000	54,000	54,000	5,887,000	4,495,000
Defined Benefit Plan, Fair Value of Plan Assets				45,406,000	36,783,000	36,990,000	2,985,000	7,133,000	6,465,000	6,475,000			3,612,000	3,149,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate				4.00%	5.00%		4.00%	4.00%	4.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets				7.00%	7.00%	8.00%	8.50%	5.00%	5.00%	5.00%
Life-Time Benefit Limit on PBOP		100,000
2011 Periodic Benefit Cost Savings from Life Time Benefit Limit of PBOP	488,000
Defined Benefit Plan, Amortization of Gains (Losses)				(1,753,000)	(687,000)	(602,000)		(851,000)	(1,128,000)	(983,000)			(634,000)	(409,000)	(423,000)
Defined Contribution Plan, Cost Recognized		$ 485,000	$ 419,000