Securities (Amortized Cost and Fair Value of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Securities [Abstract]
Debt Securities Available for Sale, Due in one year or less, Amortized Cost	$ 7,945
Debt Securities Available for Sale, Due after one year through five years, Amortized Cost	38,273
Debt Securities Available for Sale, Due after five years through ten years, Amortized Cost	997,109
Debt Securities Available for Sale, Due after ten years, Amortized Cost	1,781,460
Total available for sale debt securities, Amortized Cost	2,824,787
Debt Securities Available for Sale, Due in one year or less, Fair Value	7,970
Debt Securities Available for Sale, Due after one year through five years, Fair Value	38,767
Debt Securities Available for Sale, Due after five years through ten years, Fair Value	980,311
Debt Securities Available for Sale, Due after ten years, Fair Value	1,767,334
Total available for sale debt securities, Fair Value	2,794,382
Debt Securities Held to Maturity, Due in one year or less, Amortized Cost	9,995
Debt Securities Held to Maturity, Due after one year through five years, Amortized Cost	108,634
Debt Securities Held to Maturity, Due after five years through ten years, Amortized Cost	851,644
Debt Securities Held to Maturity, Due after ten years, Amortized Cost	1,904,181
Securities Held to Maturity, Amortized Cost	2,874,454	$ 2,500,220
Debt Securities Held to Maturity, Due in one year or less, Fair Value	10,058
Debt Securities Held to Maturity, Due after one year through five years, Fair Value	109,069
Debt Securities Held to Maturity, Due after five years through ten years, Fair Value	845,017
Debt Securities Held to Maturity, Due after ten years, Fair Value	1,902,385
Total held to maturity securities, Fair Value	$ 2,866,529	$ 2,470,117