Investment Securities (Contractual Maturities and Narrative) (Details 2) - USD ($) $ in Thousands	Mar. 31, 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	$ 127,598
Due After One Year Through Five Years	182,056
Due After Five Years Through Ten Years	66,783
Due After Ten Years	22,747
Amortized Cost, Total	399,184
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Due in One Year or Less	127,372
Due After One Year Through Five Years	182,631
Due After Five Years Through Ten Years	68,353
Due After Ten Years	23,538
Fair Value, Total	401,894
Available-for-Sale: Amortized Cost	1,864,456	$ 2,022,158
Available-for-Sale: Fair Value	1,859,256	2,007,942
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis, Rolling Maturities (Abstract]
Due in One Year or Less	179,808
Due After One Year Through Five Years	311,027
Due After Five Years Through Ten Years	181,768
Due After Ten Years	7,697
Amortized Cost, Total	680,300
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Due in One Year or Less	179,302
Due After One Year Through Five Years	314,416
Due After Five Years Through Ten Years	184,499
Due After Ten Years	8,123
Fair Value, Total	686,340
Held-to-Maturity: Amortized Cost	3,668,811
Held-to-Maturity: Fair Value	3,637,496	3,413,994
Carrying value of investment securities which were pledged to secure deposits of gov't entities and repos	2,200,000	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	364,792
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	362,730
Debt Securities Issued by Government-Sponsored Enterprises
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-Sale: Amortized Cost	189	56
Available-for-Sale: Fair Value	190	56
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	396,578
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	398,964
Available-for-Sale: Amortized Cost	396,578	189,645
Available-for-Sale: Fair Value	398,964	190,442
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	1,803,146
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	1,777,846
Held-to-Maturity: Fair Value	1,777,846	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	560,506
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	555,243
Available-for-Sale: Amortized Cost	560,506	589,311
Available-for-Sale: Fair Value	555,243	578,527
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	1,010,892
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	1,004,478
Held-to-Maturity: Fair Value	1,004,478	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	143,396
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	140,425
Available-for-Sale: Amortized Cost	143,396	63,864
Available-for-Sale: Fair Value	140,425	59,380
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	174,473
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	168,832
Held-to-Maturity: Fair Value	168,832	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	1,100,480
Available-for-sale Securities, Debt Securities Issued by Government Agencies and Mortgage-Backed Securities: Fair Value	1,094,632
Available-for-Sale: Amortized Cost	1,100,480	842,820
Available-for-Sale: Fair Value	1,094,632	828,349
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-Maturity: Mortgage-Backed Securities: Amortized Cost	2,988,511
Held-to-Maturity: Mortgage-Backed Securities: Fair Value	2,951,156
Held-to-Maturity: Fair Value	$ 2,951,156	$ 2,725,516