Counterparty Risk (Cash and Cash Equivalents) (Details)	Jun. 30, 2014	Dec. 31, 2013
Bank of New York Mellon Corporation [Member]
Concentration Risk [Line Items]
Concentration risk percentage, cash and cash equivalents	45.00%	73.00%
JP Morgan Prime Money Market Premier Fund [Member]
Concentration Risk [Line Items]
Concentration risk percentage, cash and cash equivalents	34.00%	27.00%
Goldman Sachs Financial Square Treasury Instruments Fund [Member]
Concentration Risk [Line Items]
Concentration risk percentage, cash and cash equivalents	21.00%	0.00%