Securities (Amortized Cost and Fair Value of Debt Securities Available for Sale) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	$ 5,410,502	$ 4,637,610
Securities Available for Sale, Gross Unrealized Gains	238,559	52,367
Securities Available for Sale, Gross Unrealized Losses	1,746	14,673
Securities Available for Sale, Fair Value	5,647,315	4,675,304
U.S. Treasury And Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	192,077	98,320
Securities Available for Sale, Gross Unrealized Gains	6,664	652
Securities Available for Sale, Gross Unrealized Losses	125	300
Securities Available for Sale, Fair Value	198,616	98,672
Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	297,712	242,016
Securities Available for Sale, Gross Unrealized Gains	16,291	7,789
Securities Available for Sale, Gross Unrealized Losses	347
Securities Available for Sale, Fair Value	313,656	249,805
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	2,536,999	1,910,909
Securities Available for Sale, Gross Unrealized Gains	70,222	20,268
Securities Available for Sale, Gross Unrealized Losses	531	7,020
Securities Available for Sale, Fair Value	2,606,690	1,924,157
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	1,965,664	1,570,765
Securities Available for Sale, Gross Unrealized Gains	136,056	19,880
Securities Available for Sale, Gross Unrealized Losses	720	4,178
Securities Available for Sale, Fair Value	2,101,000	1,586,467
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	410,050	807,600
Securities Available for Sale, Gross Unrealized Gains	9,141	3,757
Securities Available for Sale, Gross Unrealized Losses	21	3,142
Securities Available for Sale, Fair Value	419,170	808,215
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	8,000	8,000
Securities Available for Sale, Gross Unrealized Gains	185	21
Securities Available for Sale, Gross Unrealized Losses	2	33
Securities Available for Sale, Fair Value	$ 8,183	$ 7,988

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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