Securities (Amortized Cost and Fair Value of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Securities [Abstract]
Debt Securities Available for Sale, Due in one year or less, Amortized Cost	$ 4,864
Debt Securities Available for Sale, Due after one year through five years, Amortized Cost	47,593
Debt Securities Available for Sale, Due after five years through ten years, Amortized Cost	609,897
Debt Securities Available for Sale, Due after ten years, Amortized Cost	1,707,402
Total available for sale debt securities, Amortized Cost	2,369,756
Debt Securities Available for Sale, Due in one year or less, Fair Value	4,900
Debt Securities Available for Sale, Due after one year through five years, Fair Value	48,597
Debt Securities Available for Sale, Due after five years through ten years, Fair Value	621,549
Debt Securities Available for Sale, Due after ten years, Fair Value	1,738,433
Total available for sale debt securities, Fair Value	2,413,479
Debt Securities Held to Maturity, Due in one year or less, Amortized Cost	14,982
Debt Securities Held to Maturity, Due after one year through five years, Amortized Cost	135,330
Debt Securities Held to Maturity, Due after five years through ten years, Amortized Cost	510,536
Debt Securities Held to Maturity, Due after ten years, Amortized Cost	1,767,584
Total held to maturity securities, Amortized Cost	2,428,432	$ 2,370,388
Debt Securities Held to Maturity, Due in one year or less, Fair Value	15,019
Debt Securities Held to Maturity, Due after one year through five years, Fair Value	138,737
Debt Securities Held to Maturity, Due after five years through ten years, Fair Value	517,652
Debt Securities Held to Maturity, Due after ten years, Fair Value	1,811,132
Total held to maturity securities, Fair Value	$ 2,482,540	$ 2,375,851