Commitments: (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating leases
2014	$ 5,708,000
2015	4,385,000
2016	4,385,000
2017	4,385,000
2018	4,385,000
Thereafter	2,596,000
Rental expenses	5,213,000	5,164,000	5,190,000
Nuclear Fuel
Fuel:
2014	76,200,000
2015	39,600,000
2016	29,400,000
2017	29,100,000
2018	28,200,000
Thereafter	115,200,000
Coal
Fuel:
2014	52,000,000
2015	28,000,000
2016	$ 19,000,000