Investment Securities (Contractual Maturities and Narrative) (Details 2) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis Rolling Maturity[Abstract]
Due in One Year or Less	$ 16,418
Due After One Year Through Five Years	103,115
Due After Five Years Through Ten Years	159,864
Due After Ten Years	50
Amortized Cost, Total	279,447
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Due in One Year or Less	16,457
Due After One Year Through Five Years	103,407
Due After Five Years Through Ten Years	163,197
Due After Ten Years	50
Fair Value, Total	283,111
Available-for-Sale: Amortized Cost	2,648,239	$ 2,607,636
Available-for-Sale: Fair Value	2,726,478	2,619,003
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis, Rolling Maturities (Abstract]
Due in One Year or Less	165,017
Due After One Year Through Five Years	47,606
Amortized Cost, Total	212,623
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Due in One Year or Less	166,085
Due After One Year Through Five Years	48,926
Fair Value, Total	215,011
Held-to-Maturity: Amortized Cost	3,276,829
Held-to-Maturity: Fair Value	3,374,294	3,062,882
Carrying value of investment securities which were pledged to secure deposits of gov't entities and repos	3,600,000	2,600,000
Debt Securities Issued by Government Agencies
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Amortized Cost	188,247
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	186,834
Debt Securities Issued by Government-Sponsored Enterprises
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-Sale: Amortized Cost	936	22,128
Available-for-Sale: Fair Value	1,014	22,147
Residential - Government Agencies
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Amortized Cost	1,271,399
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	1,312,347
Available-for-Sale: Amortized Cost	1,271,399	1,164,466
Available-for-Sale: Fair Value	1,312,347	1,172,826
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	910,231
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	948,581
Held-to-Maturity: Fair Value	948,581	1,075,315
Residential - U.S. Government-Sponsored Enterprises
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Amortized Cost	641,094
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	663,275
Available-for-Sale: Amortized Cost	641,094	584,272
Available-for-Sale: Fair Value	663,275	586,761
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	2,082,380
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	2,136,223
Held-to-Maturity: Fair Value	2,136,223	1,557,872
Commercial - Government Agencies
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Amortized Cost	268,052
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	280,911
Available-for-Sale: Amortized Cost	268,052	224,372
Available-for-Sale: Fair Value	280,911	224,720
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	71,595
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	74,479
Held-to-Maturity: Fair Value	74,479	83,148
Mortgage-Backed Securities
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Amortized Cost	2,180,545
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	2,256,533
Available-for-Sale: Amortized Cost	2,180,545	1,973,110
Available-for-Sale: Fair Value	2,256,533	1,984,307
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	3,064,206
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	3,159,283
Held-to-Maturity: Fair Value	$ 3,159,283	$ 2,716,335