Securities (Schedule of Contractual Maturities of Investment Securities Available for Sale) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Available-for-sale Securities [Abstract]
Due within one year, Amortized Cost	$ 124,885
Due after one year through five years, Amortized Cost	638,921
Due after five years through ten years, Amortized Cost	804,462
Due after ten years, Amortized Cost	1,195,053
Total investment securities available-for-sale, Amortized Cost	2,768,605
Due within one year, Fair Value	124,763
Due after one year through five years, Fair Value	636,860
Due after five years through ten years, Fair Value	796,611
Due after ten years, Fair Value	1,179,517
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	5,284
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	5,080
Total investment securities available-for-sale, Fair Value	$ 2,742,831