Investments (Gains (Losses) Related to Trading Securities) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Investments, Debt and Equity Securities [Abstract]
Net gains (losses) recognized during the period	$ 9,052	$ (31,965)	$ 17,678	$ (26,613)
Less: net gains (losses) recognized during the period on trading securities sold during the period	1,411	1,059	(11,285)	7,612
Unrealized gains (losses) recognized during the period on trading securities held	$ 7,641	$ (33,024)	$ 28,963	$ (34,225)