Investment Securities (Schedule of Maturities of Investment Securities Available for Sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	$ 497,286
Due after one year through five years, Amortized Cost	2,583,970
Due after five years through ten years, Amortized Cost	1,176,355
Due after ten years, Amortized Cost	351,764
Mutual funds and preferred stocks with no stated maturity, Amortized Cost	75,895
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	84,482
Amortized Cost	4,685,270	$ 4,474,490
Due in one year or less, Fair Value	511,266
Due after one year through five years, Fair Value	2,630,865
Due after five years through ten years, Fair Value	1,202,951
Due after ten years, Fair Value	368,136
Fair Value	4,797,700	4,585,694
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	75,895	96,294
Fair Value	$ 84,482	$ 105,442