Investment Securities Available for Sale (Summary Of Available For Sale Investment Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 4,066,601	$ 4,038,239
Gross Unrealized Gains	672	6,107
Gross Unrealized Losses	(137,311)	(57,277)
Fair Value	3,929,962	3,987,069
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	122,800	83,608
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2,167)	(934)
Fair Value	120,633	82,674
U.S. Government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	40,753	10,771
Gross Unrealized Gains	181	91
Gross Unrealized Losses	0	0
Fair Value	40,934	10,862
Mortgage-backed securities issued by U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	111,406	121,283
Gross Unrealized Gains	107	519
Gross Unrealized Losses	(3,569)	(1,362)
Fair Value	107,944	120,440
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,614,668	2,666,818
Gross Unrealized Gains	59	5,059
Gross Unrealized Losses	(87,882)	(31,354)
Fair Value	2,526,845	2,640,523
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,159,859	1,135,259
Gross Unrealized Gains	139	144
Gross Unrealized Losses	(43,550)	(23,404)
Fair Value	1,116,448	1,111,999
State and municipal securities
Debt Securities, Available-for-sale [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
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	17,000	20,320
Gross Unrealized Gains	186	294
Gross Unrealized Losses	(143)	(223)
Fair Value	$ 17,043	$ 20,391