Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014 MMBTU		Mar. 31, 2014 Interest Rate Swap [Member]	Dec. 31, 2013 Natural Gas Commodity Contract [Member] MMBTU
Interest Rate Derivatives [Abstract]
Amount of accumulated other comprehensive gains (losses) related to interest rate derivatives expected to be reclassified into earnings within the next twelve months			$ (0.1)
Gross Notional Amounts of Commodity Options [Abstract]
Notional amount	0	[1],[2]		987,000	[1],[2]

[1] Amounts are not reflective of net positions in the underlying commodities.

[2] Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.