Securities (Amortized Cost and Fair Value of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Securities [Abstract]
Debt Securities Available for Sale, Due in one year or less, Amortized Cost	$ 6,825
Debt Securities Available for Sale, Due after one year through five years, Amortized Cost	53,816
Debt Securities Available for Sale, Due after five years through ten years, Amortized Cost	391,388
Debt Securities Available for Sale, Due after ten years, Amortized Cost	1,808,372
Total available for sale debt securities, Amortized Cost	2,260,401
Debt Securities Available for Sale, Due in one year or less, Fair Value	6,839
Debt Securities Available for Sale, Due after one year through five years, Fair Value	54,914
Debt Securities Available for Sale, Due after five years through ten years, Fair Value	405,008
Debt Securities Available for Sale, Due after ten years, Fair Value	1,840,839
Total available for sale debt securities, Fair Value	2,307,600
Debt Securities Held to Maturity, Due in one year or less, Amortized Cost	15,700
Debt Securities Held to Maturity, Due after one year through five years, Amortized Cost	136,327
Debt Securities Held to Maturity, Due after five years through ten years, Amortized Cost	403,112
Debt Securities Held to Maturity, Due after ten years, Amortized Cost	1,942,419
Total held to maturity securities, Amortized Cost	2,497,558	$ 2,370,388
Debt Securities Held to Maturity, Due in one year or less, Fair Value	15,779
Debt Securities Held to Maturity, Due after one year through five years, Fair Value	140,424
Debt Securities Held to Maturity, Due after five years through ten years, Fair Value	416,795
Debt Securities Held to Maturity, Due after ten years, Fair Value	1,996,086
Total held to maturity securities, Fair Value	$ 2,569,084	$ 2,375,851