Financial Instruments (Details 3) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Investments, Debt and Equity Securities [Abstract]
Proceeds from maturities and sales	$ 601,900	$ 560,100	$ 975,517	$ 1,317,525
Realized gains	300	200	500	400
Realized losses	$ (500)	$ (100)	$ (800)	$ (200)