Investment Securities (Amortization Cost, Gross Unrealized Gains/Losses, and Fair Value) (Details 1) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Available-for-Sale:
Available-for-Sale: Amortized Cost	$ 2,648,239	$ 2,607,636
Available-for-Sale: Gross Unrealized Gains	81,888	21,143
Available-for-Sale: Gross Unrealized Losses	(3,649)	(9,776)
Available-for-Sale	2,726,478	2,619,003
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	3,276,829	3,042,294
Held-to-Maturity: Gross Unrealized Gains	97,895	29,990
Held-to-Maturity: Gross Unrealized Losses	(430)	(9,402)
Held-to-Maturity: Fair Value	3,374,294	3,062,882
Debt Securities Issued by Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	936	22,128
Available-for-Sale: Gross Unrealized Gains	78	19
Available-for-Sale: Gross Unrealized Losses	0	0
Available-for-Sale	1,014	22,147
Residential - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	1,271,399	1,164,466
Available-for-Sale: Gross Unrealized Gains	41,364	11,627
Available-for-Sale: Gross Unrealized Losses	(416)	(3,267)
Available-for-Sale	1,312,347	1,172,826
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	910,231	1,067,416
Held-to-Maturity: Gross Unrealized Gains	38,360	13,247
Held-to-Maturity: Gross Unrealized Losses	(10)	(5,348)
Held-to-Maturity: Fair Value	948,581	1,075,315
Residential - U.S. Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	641,094	584,272
Available-for-Sale: Gross Unrealized Gains	22,206	4,363
Available-for-Sale: Gross Unrealized Losses	(25)	(1,874)
Available-for-Sale	663,275	586,761
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	2,082,380	1,546,479
Held-to-Maturity: Gross Unrealized Gains	54,263	13,871
Held-to-Maturity: Gross Unrealized Losses	(420)	(2,478)
Held-to-Maturity: Fair Value	2,136,223	1,557,872
Commercial - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	268,052	224,372
Available-for-Sale: Gross Unrealized Gains	12,859	2,889
Available-for-Sale: Gross Unrealized Losses	0	(2,541)
Available-for-Sale	280,911	224,720
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	71,595	84,238
Held-to-Maturity: Gross Unrealized Gains	2,884	317
Held-to-Maturity: Gross Unrealized Losses	0	(1,407)
Held-to-Maturity: Fair Value	74,479	83,148
Mortgage-Backed Securities
Available-for-Sale:
Available-for-Sale: Amortized Cost	2,180,545	1,973,110
Available-for-Sale: Gross Unrealized Gains	76,429	18,879
Available-for-Sale: Gross Unrealized Losses	(441)	(7,682)
Available-for-Sale	2,256,533	1,984,307
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	3,064,206	2,698,133
Held-to-Maturity: Gross Unrealized Gains	95,507	27,435
Held-to-Maturity: Gross Unrealized Losses	(430)	(9,233)
Held-to-Maturity: Fair Value	3,159,283	2,716,335
Debt Securities Issued by the U.S. Treasury and Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	189,337	222,365
Available-for-Sale: Gross Unrealized Gains	163	213
Available-for-Sale: Gross Unrealized Losses	(1,551)	(1,447)
Available-for-Sale	187,949	221,131
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	144,841	274,375
Held-to-Maturity: Gross Unrealized Gains	892	1,319
Held-to-Maturity: Gross Unrealized Losses	0	(31)
Held-to-Maturity: Fair Value	145,733	275,663
Debt Securities Issued by States and Political Subdivisions
Available-for-Sale:
Available-for-Sale: Amortized Cost	54,274	54,480
Available-for-Sale: Gross Unrealized Gains	1,328	631
Available-for-Sale: Gross Unrealized Losses	0	(14)
Available-for-Sale	55,602	55,097
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	54,273	54,811
Held-to-Maturity: Gross Unrealized Gains	1,286	1,236
Held-to-Maturity: Gross Unrealized Losses	0	0
Held-to-Maturity: Fair Value	55,559	56,047
Debt Securities Issued by Corporations
Available-for-Sale:
Available-for-Sale: Amortized Cost	223,147	335,553
Available-for-Sale: Gross Unrealized Gains	3,890	1,401
Available-for-Sale: Gross Unrealized Losses	(1,657)	(633)
Available-for-Sale	225,380	336,321
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	13,509	14,975
Held-to-Maturity: Gross Unrealized Gains	210	0
Held-to-Maturity: Gross Unrealized Losses	0	(138)
Held-to-Maturity: Fair Value	$ 13,719	$ 14,837

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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