Gross Gains and Losses from Investment Sales (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments Debt And Equity Securities [Abstract]
Gross gains	$ 36,805	$ 15,821	$ 18,717
Gross losses	(4,074)	(10,625)	(301,729)
Net gain (loss)	$ 32,731	$ 5,196	$ (283,012)