Securities (Amortized Cost and Fair Value of Debt Securities Available for Sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	$ 4,698,304	$ 4,637,610
Securities Available for Sale, Gross Unrealized Gains	233,985	52,367
Securities Available for Sale, Gross Unrealized Losses	147	14,673
Securities Available for Sale, Fair Value	4,932,142	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	142,265	98,320
Securities Available for Sale, Gross Unrealized Gains	6,351	652
Securities Available for Sale, Gross Unrealized Losses		300
Securities Available for Sale, Fair Value	148,616	98,672
Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	239,922	242,016
Securities Available for Sale, Gross Unrealized Gains	14,764	7,789
Securities Available for Sale, Fair Value	254,686	249,805
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	2,007,247	1,910,909
Securities Available for Sale, Gross Unrealized Gains	70,089	20,268
Securities Available for Sale, Gross Unrealized Losses	13	7,020
Securities Available for Sale, Fair Value	2,077,323	1,924,157
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	1,726,091	1,570,765
Securities Available for Sale, Gross Unrealized Gains	132,398	19,880
Securities Available for Sale, Gross Unrealized Losses		4,178
Securities Available for Sale, Fair Value	1,858,489	1,586,467
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	574,779	807,600
Securities Available for Sale, Gross Unrealized Gains	10,158	3,757
Securities Available for Sale, Gross Unrealized Losses	115	3,142
Securities Available for Sale, Fair Value	584,822	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	225	21
Securities Available for Sale, Gross Unrealized Losses	19	33
Securities Available for Sale, Fair Value	$ 8,206	$ 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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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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