Investments (Gains (Losses) Related to Trading Securities) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Investments, Debt and Equity Securities [Abstract]
Net gains (losses) recognized during the period	$ 7,394	$ (1,432)	$ 8,626	$ 5,352
Less: net (losses) gains recognized during the period on trading securities sold during the period	(2,335)	506	(12,696)	6,553
Unrealized gains (losses) recognized during the period on trading securities held	$ 9,729	$ (1,938)	$ 21,322	$ (1,201)