Significant Accounting Policies - Cash and Cash Equivalents (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Cash Held by Broker as Margin on Eurodollar Futures Contracts	$ 8,663,000	$ 5,174,000
Cash Held on Deposit with Repurchase Agreement Counterparties	14,397,000	$ 2,616,000
Uninsured Cash Balances	99,800,000
Insurance per depositor at each financial institution	$ 250,000