Securities (Amortized Cost and Fair Value of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Securities [Abstract]
Debt Securities Available for Sale, Due in one year or less, Amortized Cost	$ 6,851
Debt Securities Available for Sale, Due after one year through five years, Amortized Cost	78,862
Debt Securities Available for Sale, Due after five years through ten years, Amortized Cost	366,738
Debt Securities Available for Sale, Due after ten years, Amortized Cost	1,661,371
Total available for sale debt securities, Amortized Cost	2,113,822
Debt Securities Available for Sale, Due in one year or less, Fair Value	6,881
Debt Securities Available for Sale, Due after one year through five years, Fair Value	79,865
Debt Securities Available for Sale, Due after five years through ten years, Fair Value	377,314
Debt Securities Available for Sale, Due after ten years, Fair Value	1,682,644
Total available for sale debt securities, Fair Value	2,146,704
Debt Securities Held to Maturity, Due in one year or less, Amortized Cost	15,296
Debt Securities Held to Maturity, Due after one year through five years, Amortized Cost	415,949
Debt Securities Held to Maturity, Due after five years through ten years, Amortized Cost	356,084
Debt Securities Held to Maturity, Due after ten years, Amortized Cost	1,731,042
Total held to maturity securities, Amortized Cost	2,518,371	$ 2,370,388
Debt Securities Held to Maturity, Due in one year or less, Fair Value	15,408
Debt Securities Held to Maturity, Due after one year through five years, Fair Value	417,841
Debt Securities Held to Maturity, Due after five years through ten years, Fair Value	358,834
Debt Securities Held to Maturity, Due after ten years, Fair Value	1,774,716
Total held to maturity securities, Fair Value	$ 2,566,799	$ 2,375,851