Investments (Gains (Losses) Related to Trading Securities) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]
Net (losses) gains recognized during the period	$ (31,965)	$ (14,784)	$ (26,613)	$ 10,985
Less: net gains recognized during the period on trading securities sold during the period	1,059	3,580	7,612	11,446
Unrealized (losses) recognized during the period on trading securities held	$ (33,024)	$ (18,364)	$ (34,225)	$ (461)