Guarantees (Details 3) (USD $)	Jun. 30, 2014
Guarantor Obligations [Line Items]
Amount of hedging obligations guaranteed reflected on balance sheet	$ 14,500,000
Guarantor obligations, maximum exposure, undiscounted	76,700,000
Fixed maximum amounts guaranteed by year 2014	21,200,000
Fixed maximum amounts guaranteed by year 2015	35,700,000
Fixed maximum amounts guaranteed by year 2016	700,000
Fixed maximum amounts guaranteed by year 2017	600,000
Fixed maximum amounts guaranteed by year 2018	500,000
Fixed maximum amounts guaranteed by year 2019	500,000
Fixed maximum amounts guaranteed by year expires after certain number of days after written notice	13,500,000
No scheduled maturity date	4,000,000
Amount outstanding under guarantees that is reflected on balance sheet	200,000
Letters of credit	36,300,000
Letters of credit set to expire - 2014	7,000,000
Letters of credit set to expire - 2015	29,300,000
Outstanding letters of credit	0
Natural gas transportation and storage agreement fixed maximum amount of performance guarantee of a related party	4,000,000
Amount outstanding by a related party under the guarantee	1,100,000
Amount of surety bonds outstanding	$ 666,900,000