Investment Securities (Contractual Maturities and Narrative) (Details 2) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis Rolling Maturity[Abstract]
Due in One Year or Less	$ 169,659
Due After One Year Through Five Years	107,258
Due After Five Years Through Ten Years	135,099
Due After Ten Years	52
Amortized Cost, Total	412,068
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Due in One Year or Less	169,782
Due After One Year Through Five Years	107,298
Due After Five Years Through Ten Years	136,099
Due After Ten Years	52
Fair Value, Total	413,231
Available-for-Sale: Amortized Cost	2,637,898	$ 2,022,158
Available-for-Sale: Fair Value	2,649,949	2,007,942
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis, Rolling Maturities (Abstract]
Due in One Year or Less	219,851
Due After One Year Through Five Years	199,291
Due After Five Years Through Ten Years	16,429
Due After Ten Years	0
Amortized Cost, Total	435,571
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Due in One Year or Less	220,115
Due After One Year Through Five Years	201,922
Due After Five Years Through Ten Years	16,195
Due After Ten Years	0
Fair Value, Total	438,232
Held-to-Maturity: Amortized Cost	2,959,611
Held-to-Maturity: Fair Value	2,973,229	3,413,994
Carrying value of investment securities which were pledged to secure deposits of gov't entities and repos	2,500,000	2,300,000
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	335,479
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	334,528
Debt Securities Issued by Government-Sponsored Enterprises
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-Sale: Amortized Cost	192	56
Available-for-Sale: Fair Value	196
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	1,219,120
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	1,227,930
Available-for-Sale: Amortized Cost	1,219,120	189,645
Available-for-Sale: Fair Value	1,227,930	190,442
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	1,219,447
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	1,225,189
Held-to-Maturity: Fair Value	1,225,189	1,813,987
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	500,664
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	503,057
Available-for-Sale: Amortized Cost	500,664	589,311
Available-for-Sale: Fair Value	503,057	578,527
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	1,218,431
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	1,225,294
Held-to-Maturity: Fair Value	1,225,294	740,166
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	170,567
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	171,203
Available-for-Sale: Amortized Cost	170,567	63,864
Available-for-Sale: Fair Value	171,203	59,380
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	86,162
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	84,514
Held-to-Maturity: Fair Value	84,514	171,363
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	1,890,351
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	1,902,190
Available-for-Sale: Amortized Cost	1,890,351	842,820
Available-for-Sale: Fair Value	1,902,190	828,349
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	2,524,040
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	2,534,997
Held-to-Maturity: Fair Value	$ 2,534,997	$ 2,725,516