Investment Securities (Amort cost, unrealized gains and losses, and fair value) (Details 1) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity: Amortized Cost	$ 3,042,294	$ 3,482,092	$ 3,928,170
Held-to-Maturity: Gross Unrealized Gains	29,990	11,959	20,949
Held-to-Maturity: Gross Unrealized Losses	(9,402)	(80,057)	(54,998)
Held-to-Maturity: Fair Value	3,062,882	3,413,994	3,894,121
Available-for-Sale:
Debt Securities, Available-for-sale, Amortized Cost	2,607,636	2,022,158	2,236,144
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	21,143	9,225	15,695
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	9,776	23,441	18,860
Debt Securities, Available-for-sale	2,619,003	2,007,942	2,232,979
Available-for-sale Securities, Amortized Cost Basis	2,607,636
Available-for-Sale	2,619,003	2,007,942
Debt Securities Issued by the U.S. Treasury and Government Agencies
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity: Amortized Cost	274,375	353,122	375,074
Held-to-Maturity: Gross Unrealized Gains	1,319	186	18
Held-to-Maturity: Gross Unrealized Losses	(31)	(1,093)	(1,451)
Held-to-Maturity: Fair Value	275,663	352,215	373,641
Available-for-Sale:
Debt Securities, Available-for-sale, Amortized Cost	222,365	394,485	424,912
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	213	493	2,053
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,447	2,577	1,035
Debt Securities, Available-for-sale	221,131	392,401	425,930
Debt Securities Issued by States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity: Amortized Cost	54,811	234,602	238,504
Held-to-Maturity: Gross Unrealized Gains	1,236	6,150	9,125
Held-to-Maturity: Gross Unrealized Losses	0	0	0
Held-to-Maturity: Fair Value	56,047	240,752	247,629
Available-for-Sale:
Debt Securities, Available-for-sale, Amortized Cost	54,480	559,800	618,167
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	631	5,227	9,894
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	14	1,031	1,042
Debt Securities, Available-for-sale	55,097	563,996	627,019
US Government-sponsored Enterprises Debt Securities [Member]
Available-for-Sale:
Debt Securities, Available-for-sale, Amortized Cost	22,128
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	19
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0
Debt Securities, Available-for-sale	22,147
Available-for-sale Securities, Amortized Cost Basis		56
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		0
Available-for-Sale		56
Debt Securities Issued by Corporations
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity: Amortized Cost	14,975	97,266	119,635
Held-to-Maturity: Gross Unrealized Gains	0	0	123
Held-to-Maturity: Gross Unrealized Losses	(138)	(1,755)	(1,591)
Held-to-Maturity: Fair Value	14,837	95,511	118,167
Available-for-Sale:
Debt Securities, Available-for-sale, Amortized Cost	335,553	224,997	268,003
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1,401	0	199
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	633	1,857	2,091
Debt Securities, Available-for-sale	336,321	223,140	266,111
Mortgage-Backed Securities
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity: Amortized Cost	2,698,133	2,797,102	3,194,957
Held-to-Maturity: Gross Unrealized Gains	27,435	5,623	11,683
Held-to-Maturity: Gross Unrealized Losses	(9,233)	(77,209)	(51,956)
Held-to-Maturity: Fair Value	2,716,335	2,725,516	3,154,684
Available-for-Sale:
Debt Securities, Available-for-sale, Amortized Cost	1,973,110	842,820	925,062
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	18,879	3,505	3,549
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	7,682	17,976	14,692
Debt Securities, Available-for-sale	1,984,307	828,349	913,919
Residential - Government Agencies
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity: Amortized Cost	1,067,416	1,861,874	2,229,985
Held-to-Maturity: Gross Unrealized Gains	13,247	3,886	9,975
Held-to-Maturity: Gross Unrealized Losses	(5,348)	(51,773)	(37,047)
Held-to-Maturity: Fair Value	1,075,315	1,813,987	2,202,913
Available-for-Sale:
Debt Securities, Available-for-sale, Amortized Cost	1,164,466	189,645	233,268
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	11,627	1,726	3,129
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	3,267	929	1,037
Debt Securities, Available-for-sale	1,172,826	190,442	235,360
Residential - U.S. Government Sponsored Enterprises
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity: Amortized Cost	1,546,479	758,835	763,312
Held-to-Maturity: Gross Unrealized Gains	13,871	1,590	911
Held-to-Maturity: Gross Unrealized Losses	(2,478)	(20,259)	(11,255)
Held-to-Maturity: Fair Value	1,557,872	740,166	752,968
Available-for-Sale:
Debt Securities, Available-for-sale, Amortized Cost	584,272	589,311	619,795
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	4,363	1,779	420
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,874	12,563	10,403
Debt Securities, Available-for-sale	586,761	578,527	609,812
Commercial - Government Agencies
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity: Amortized Cost	84,238	176,393	201,660
Held-to-Maturity: Gross Unrealized Gains	317	147	797
Held-to-Maturity: Gross Unrealized Losses	(1,407)	(5,177)	(3,654)
Held-to-Maturity: Fair Value	83,148	171,363	198,803
Available-for-Sale:
Debt Securities, Available-for-sale, Amortized Cost	224,372	63,864	71,999
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2,889	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2,541	4,484	3,252
Debt Securities, Available-for-sale	$ 224,720	$ 59,380	$ 68,747