Securities (Amortized Cost and Fair Value of Debt Securities Available for Sale) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	$ 6,609,893	$ 5,766,234
Securities Available for Sale, Gross Unrealized Gains	147,275	236,826
Securities Available for Sale, Gross Unrealized Losses	126,520	3,733
Securities Available for Sale, Fair Value	6,630,648	5,999,327
U.S. Treasury And Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	219,343	207,365
Securities Available for Sale, Gross Unrealized Gains	2,703	6,289
Securities Available for Sale, Gross Unrealized Losses	4,554	284
Securities Available for Sale, Fair Value	217,492	213,370
Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	308,298	309,342
Securities Available for Sale, Gross Unrealized Gains	13,757	17,536
Securities Available for Sale, Gross Unrealized Losses	5,393	153
Securities Available for Sale, Fair Value	316,662	326,725
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	2,976,621	2,560,249
Securities Available for Sale, Gross Unrealized Gains	45,861	69,570
Securities Available for Sale, Gross Unrealized Losses	51,672	8
Securities Available for Sale, Fair Value	2,970,810	2,629,811
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	2,789,053	2,323,306
Securities Available for Sale, Gross Unrealized Gains	78,043	135,516
Securities Available for Sale, Gross Unrealized Losses	64,901	3,288
Securities Available for Sale, Fair Value	2,802,195	2,455,534
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	305,078	354,472
Securities Available for Sale, Gross Unrealized Gains	6,835	7,651
Securities Available for Sale, Fair Value	311,913	362,123
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	11,500	11,500
Securities Available for Sale, Gross Unrealized Gains	76	264
Securities Available for Sale, Fair Value	$ 11,576	$ 11,764

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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Amount 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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