Investment Securities (Summary Of Available For Sale Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 4,103,438	$ 4,038,239
Gross Unrealized Gains	1,122	6,107
Gross Unrealized Losses	(113,582)	(57,277)
Fair Value	3,990,978	3,987,069
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	122,655	83,608
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,724)	(934)
Fair Value	120,931	82,674
U.S. Government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,769	10,771
Gross Unrealized Gains	128	91
Gross Unrealized Losses	0	0
Fair Value	10,897	10,862
Mortgage-backed securities issued by U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	115,888	121,283
Gross Unrealized Gains	237	519
Gross Unrealized Losses	(3,257)	(1,362)
Fair Value	112,868	120,440
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,734,650	2,666,818
Gross Unrealized Gains	483	5,059
Gross Unrealized Losses	(71,133)	(31,354)
Fair Value	2,664,000	2,640,523
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,102,361	1,135,259
Gross Unrealized Gains	0	144
Gross Unrealized Losses	(37,320)	(23,404)
Fair Value	1,065,041	1,111,999
State and municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	115	180
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	115	180
Corporate debt and other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,000	20,320
Gross Unrealized Gains	274	294
Gross Unrealized Losses	(148)	(223)
Fair Value	$ 17,126	$ 20,391