Investment Securities (Contractual Maturities and Narrative) (Details 2) - USD ($) $ in Thousands	Mar. 31, 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	$ 66,246
Due After One Year Through Five Years	96,977
Due After Five Years Through Ten Years	167,141
Due After Ten Years	50
Amortized Cost, Total	330,414
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Due in One Year or Less	66,355
Due After One Year Through Five Years	95,275
Due After Five Years Through Ten Years	166,707
Due After Ten Years	51
Fair Value, Total	328,388
Available-for-Sale: Amortized Cost	2,613,203	$ 2,607,636
Available-for-Sale: Fair Value	2,681,049	2,619,003
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis, Rolling Maturities (Abstract]
Due in One Year or Less	234,892
Due After One Year Through Five Years	48,506
Amortized Cost, Total	283,398
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Due in One Year or Less	237,171
Due After One Year Through Five Years	49,459
Fair Value, Total	286,630
Held-to-Maturity: Amortized Cost	3,004,139
Held-to-Maturity: Fair Value	3,104,020	3,062,882
Carrying value of investment securities which were pledged to secure deposits of gov't entities and repos	3,400,000	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	200,921
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	199,912
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	1,012	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	1,159,266
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	1,199,214
Available-for-Sale: Amortized Cost	1,159,266	1,164,466
Available-for-Sale: Fair Value	1,199,214	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	994,405
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	1,033,047
Held-to-Maturity: Fair Value	1,033,047	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	635,161
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	661,173
Available-for-Sale: Amortized Cost	635,161	584,272
Available-for-Sale: Fair Value	661,173	586,761
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	1,648,144
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	1,705,698
Held-to-Maturity: Fair Value	1,705,698	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	287,441
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	292,362
Available-for-Sale: Amortized Cost	287,441	224,372
Available-for-Sale: Fair Value	292,362	224,720
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	78,192
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	78,645
Held-to-Maturity: Fair Value	78,645	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	2,081,868
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	2,152,749
Available-for-Sale: Amortized Cost	2,081,868	1,973,110
Available-for-Sale: Fair Value	2,152,749	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	2,720,741
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	2,817,390
Held-to-Maturity: Fair Value	$ 2,817,390	$ 2,716,335