Summary of Significant Accounting Policies (Reconciliation of Net Income to Taxable Income Before Dividends Paid Deduction) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Net income (loss)	$ 315,278	$ 621,861	$ 246,455
Book/tax differences	(61,138)	(316,097)	738
Taxable income before adjustments	254,140	305,764	247,193
Less: capital gains	(63,196)	(294,901)	(95,797)
Adjusted taxable income subject to 90% distribution requirement	$ 190,944	$ 10,863	$ 151,396