Investment Securities (Schedule of Maturities of Investment Securities Available for Sale) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	$ 561,441
Due after one year through five years, Amortized Cost	3,113,496
Due after five years through ten years, Amortized Cost	1,933,476
Due after ten years, Amortized Cost	311,610
Preferred stocks with no stated maturity	76,180
Amortized Cost	5,996,203	$ 4,791,284
Due in one year or less, Fair Value	574,582
Due after one year through five years, Fair Value	3,143,551
Due after five years through ten years, Fair Value	1,941,201
Due after ten years, Fair Value	326,047
Preferred Stocks with no stated maturity, Fair Value	88,203
Fair Value	6,073,584	4,859,539
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	76,180	75,742
Fair Value	$ 88,203	$ 83,209