Securities (Securities Held to Maturity with Unrealized Losses) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	$ 1,666,658	$ 1,513,235
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	20,440	34,152
Held to maturity, Losses 12 months or longer, Fair Value	141,333	127,125
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	3,782	3,847
Held to maturity, Total, Fair Value	1,807,991	1,640,360
Held to maturity, Total, Gross Unrealized Losses	24,222	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	49,936	49,956
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	64	44
Held to maturity, Total, Fair Value	49,936	49,956
Held to maturity, Total, Gross Unrealized Losses	64	44
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	432,877	494,470
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	9,311	19,706
Held to maturity, Losses 12 months or longer, Fair Value	7,204	11,750
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	303	469
Held to maturity, Total, Fair Value	440,081	506,220
Held to maturity, Total, Gross Unrealized Losses	9,614	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	268,110	278,369
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	1,315	3,068
Held to maturity, Total, Fair Value	268,110	278,369
Held to maturity, Total, Gross Unrealized Losses	1,315	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	73,068	71,701
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	2,637	4,038
Held to maturity, Total, Fair Value	73,068	71,701
Held to maturity, Total, Gross Unrealized Losses	2,637	4,038
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	842,667	618,739
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	7,113	7,296
Held to maturity, Losses 12 months or longer, Fair Value	134,129	115,375
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	3,479	3,378
Held to maturity, Total, Fair Value	976,796	734,114
Held to maturity, Total, Gross Unrealized Losses	$ 10,592	$ 10,674