Fair Value: (Details 2) (USD $)			1 Months Ended			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Feb. 29, 2012 Loss on auction rate securities	Feb. 29, 2012 Auction rate securities	Feb. 15, 2012 Auction rate securities	Dec. 31, 2012 Decommissioning funds	Dec. 31, 2012 Long-term investments	Dec. 31, 2013 Interest rate options	Dec. 31, 2012 Interest rate options
Assets (Liabilities):
Balance at the beginning of the period						$ (982,000)	$ 7,713,000	$ 25,783,000	$ 69,446,000
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)						982,000	887,000	37,688,000	(43,663,000)
Purchases, issuances, liquidations							(8,600,000)
Balance at the end of the period								63,471,000	25,783,000
Investments sold	359,797,000	330,627,000			8,600,000
Loss on sale of investments				$ 1,075,000
Period over which loss is charged to income			P4Y