Securities (Amortized Cost and Fair Value of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Securities [Abstract]
Debt Securities Available for Sale, Due in one year or less, Amortized Cost	$ 4,711
Debt Securities Available for Sale, Due after one year through five years, Amortized Cost	40,658
Debt Securities Available for Sale, Due after five years through ten years, Amortized Cost	1,025,204
Debt Securities Available for Sale, Due after ten years, Amortized Cost	1,470,962
Total available for sale debt securities, Amortized Cost	2,541,535
Debt Securities Available for Sale, Due in one year or less, Fair Value	4,735
Debt Securities Available for Sale, Due after one year through five years, Fair Value	41,205
Debt Securities Available for Sale, Due after five years through ten years, Fair Value	999,011
Debt Securities Available for Sale, Due after ten years, Fair Value	1,453,810
Total available for sale debt securities, Fair Value	2,498,761
Debt Securities Held to Maturity, Due in one year or less, Amortized Cost	10,520
Debt Securities Held to Maturity, Due after one year through five years, Amortized Cost	124,250
Debt Securities Held to Maturity, Due after five years through ten years, Amortized Cost	838,244
Debt Securities Held to Maturity, Due after ten years, Amortized Cost	1,529,498
Securities Held to Maturity, Amortized Cost	2,502,512	$ 2,500,220
Debt Securities Held to Maturity, Due in one year or less, Fair Value	10,624
Debt Securities Held to Maturity, Due after one year through five years, Fair Value	125,558
Debt Securities Held to Maturity, Due after five years through ten years, Fair Value	817,979
Debt Securities Held to Maturity, Due after ten years, Fair Value	1,523,259
Total held to maturity securities, Fair Value	$ 2,477,420	$ 2,470,117