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, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
REIT dividend distribution requirement percentage	90.00%
Net income (loss)	$ 432,644	$ 387,268	$ 1,654,341
Book/tax differences	(118,481)	(97,079)	(1,073,552)
Taxable income before adjustments	314,163	290,189	580,789
Less: capital gains	(61,531)	(63,151)	(441,577)
Adjusted taxable income subject to 90% distribution requirement	$ 252,632	$ 227,038	$ 139,212