Securities (Schedule of Book Values and Fair Values of Investment Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Amortized Cost
Due within one year	$ 0
Due after one year but within five years	28,650
Due after five years but within ten years	74,015
Due after ten years	11,000
Mortgage-backed securities	2,000,949
Amortized Cost	2,114,614	$ 1,432,684
Fair Value
Due within one year	0
Due after one year but within five years	29,931
Due after five years but within ten years	72,409
Due after ten years	10,494
Mortgage-backed securities	2,002,319
Total securities	2,115,153	1,453,132
Amortized Cost
Due within one year	1,262
Due after one year but within five years	537
Due after five years but within ten years	8,766
Due after ten years	256,896
Mortgage-backed securities	24,267
Amortized Cost	291,728	167,551
Fair Value
Due within one year	1,283
Due after one year but within five years	553
Due after five years but within ten years	8,825
Due after ten years	256,877
Mortgage-backed securities	25,236
Total securities	$ 292,774	$ 170,734