Fair Value Fair Value (Summary of Quantitative Information Relating to the Principal Valuation Techniques and Significant Unobservable Inputs for Level 3) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Summary of Quantitative Information Relating to the Principal Valuation Techniques and Significant Unobservable Inputs for Level 3 [Line Items]
Investment securities	$ 13,372,194	$ 7,643,116
Fair Value, Inputs, Level 3 [Member]
Summary of Quantitative Information Relating to the Principal Valuation Techniques and Significant Unobservable Inputs for Level 3 [Line Items]
Investment securities	$ 0	$ 0