Securities (Securities Held to Maturity with Unrealized Losses) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	$ 1,361,621	$ 1,513,235
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	30,057	34,152
Held to maturity, Losses 12 months or longer, Fair Value	111,280	127,125
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	3,449	3,847
Held to maturity, Total, Fair Value	1,472,901	1,640,360
Held to maturity, Total, Gross Unrealized Losses	33,506	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	49,946	49,956
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	55	44
Held to maturity, Total, Fair Value	49,946	49,956
Held to maturity, Total, Gross Unrealized Losses	55	44
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	454,266	494,470
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	17,331	19,706
Held to maturity, Losses 12 months or longer, Fair Value	7,269	11,750
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	273	469
Held to maturity, Total, Fair Value	461,535	506,220
Held to maturity, Total, Gross Unrealized Losses	17,604	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	279,443	278,369
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	1,980	3,068
Held to maturity, Total, Fair Value	279,443	278,369
Held to maturity, Total, Gross Unrealized Losses	1,980	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	71,373	71,701
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	4,348	4,038
Held to maturity, Total, Fair Value	71,373	71,701
Held to maturity, Total, Gross Unrealized Losses	4,348	4,038
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	506,593	618,739
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	6,343	7,296
Held to maturity, Losses 12 months or longer, Fair Value	104,011	115,375
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	3,176	3,378
Held to maturity, Total, Fair Value	610,604	734,114
Held to maturity, Total, Gross Unrealized Losses	$ 9,519	$ 10,674