Securities (Securities Held to Maturity with Unrealized Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	$ 768,589	$ 1,513,235
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	6,515	34,152
Held to maturity, Losses 12 months or longer, Fair Value	1,055,983	127,125
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	22,096	3,847
Held to maturity, Total, Fair Value	1,824,572	1,640,360
Held to maturity, Total, Gross Unrealized Losses	28,611	37,999
U.S. Treasury And Government Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value		49,956
Held to maturity, Losses less than 12 months, Gross Unrealized Losses		44
Held to maturity, Losses 12 months or longer, Fair Value	49,711
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	289
Held to maturity, Total, Fair Value	49,711	49,956
Held to maturity, Total, Gross Unrealized Losses	289	44
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	14,603	494,470
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	19	19,706
Held to maturity, Losses 12 months or longer, Fair Value	230,960	11,750
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	4,226	469
Held to maturity, Total, Fair Value	245,563	506,220
Held to maturity, Total, Gross Unrealized Losses	4,245	20,175
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	8,815	278,369
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	99	3,068
Held to maturity, Losses 12 months or longer, Fair Value	230,277
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	2,591
Held to maturity, Total, Fair Value	239,092	278,369
Held to maturity, Total, Gross Unrealized Losses	2,690	3,068
Commercial Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	174,882	71,701
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	744	4,038
Held to maturity, Losses 12 months or longer, Fair Value	72,499
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	3,171
Held to maturity, Total, Fair Value	247,381	71,701
Held to maturity, Total, Gross Unrealized Losses	3,915	4,038
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	570,289	618,739
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	5,653	7,296
Held to maturity, Losses 12 months or longer, Fair Value	472,536	115,375
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	11,819	3,378
Held to maturity, Total, Fair Value	1,042,825	734,114
Held to maturity, Total, Gross Unrealized Losses	$ 17,472	$ 10,674