Securities (Securities available for sale debt maturities) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Amortized Cost
Due in 1 year or less	$ 23,216
Due in 1 to 5 years	50,520
Due in 5 to 10 years	131,431
Due after 10 years	194,091
Total debt securities	399,258
Mortgage and asset-backed securities	1,926,803
Equity securities with a readily determinable fair value	16,916
Amortized Cost	2,342,977	$ 2,248,181
Estimated Fair Value
Due in 1 year or less	23,161
Due in 1 to 5 years	49,592
Due in 5 to 10 years	125,824
Due after 10 years	186,903
Total debt securities	385,480
Mortgage and asset-backed securities	1,871,819
Equity securities with a readily determinable fair value	16,916
Estimated Fair Value	$ 2,274,215	$ 2,216,753