Investment Securities - Debt Maturities (Details) - Investment Securities [Member] - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Available-for-sale Securities, Due within one year, Amortized Cost	$ 1,222,236
Available-for-sale Securities, Due after one year through five years, Amortized Cost	146,389
Available-for-sale Securities, Due after five years through ten years, Amortized Cost	575,023
Available-for-sale Securities, Due after ten years, Amortized Cost	835,399
Available-for-sale Securities, Debt Maturities, Single Maturity Date [Abstract]
Available-for-sale Securities, Due within one year, Fair Value	1,221,760
Available-for-sale Securities, Due after one year through five years, Fair Value	147,101
Available-for-sale Securities, Due after five years through ten years, Fair Value	573,082
Available-for-sale Securities, Due after ten years, Fair Value	833,082
Available-for-sale securities	$ 2,775,025	$ 1,938,499
Available-for-sale Securities, Debt Maturities, Weighted Average Yield, Single Maturity Date [Abstract]
Available-for-sale Securities, Due within one year, Weighted-Average Yield	0.43%
Available-for-sale Securities, Due after one year through five years, Weighted-Average Yield	1.10%
Available-for-sale Securities, Due after five years through ten years, Weighted-Average Yield	0.86%
Available-for-sale Securities, Due after ten years, Weighted-Average Yield	0.90%
Available-for-sale Securities, Total Weighted-Average Yield	0.70%