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, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Net income (loss)	$ 621,861	$ 246,455	$ 196,549
Book/tax differences	(314,691)	738	50,127
Taxable income before adjustments	307,170	247,193	246,676
Less: capital gains	(294,901)	(95,797)	(109,133)
Adjusted taxable income subject to 90% distribution requirement	$ 12,269	$ 151,396	$ 137,543