Investment Securities - Debt Maturities (Details) (Investment Securities [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investment Securities [Member]
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Available-for-sale Securities, Due within one year, Amortized Cost	$ 954,530
Available-for-sale Securities, Due after one year through five years, Amortized Cost	158,655
Available-for-sale Securities, Due after five years through ten years, Amortized Cost	288,764
Available-for-sale Securities, Due after ten years, Amortized Cost	586,428
Available-for-sale Securities, Debt Maturities, Single Maturity Date [Abstract]
Available-for-sale Securities, Due within one year, Fair Value	954,742
Available-for-sale Securities, Due after one year through five years, Fair Value	159,441
Available-for-sale Securities, Due after five years through ten years, Fair Value	286,868
Available-for-sale Securities, Due after ten years, Fair Value	583,932
Available-for-sale securities	$ 1,984,983	$ 2,483,147
Available-for-sale Securities, Debt Maturities, Weighted Average Yield, Single Maturity Date [Abstract]
Available-for-sale Securities, Due within one year, Weighted-Average Yield	0.28%
Available-for-sale Securities, Due after one year through five years, Weighted-Average Yield	0.92%
Available-for-sale Securities, Due after five years through ten years, Weighted-Average Yield	0.78%
Available-for-sale Securities, Due after ten years, Weighted-Average Yield	2.38%
Available-for-sale Securities, Total Weighted-Average Yield	1.02%