Securities (Amortized Cost and Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	$ 2,502,512	$ 2,500,220
Securities Held to Maturity, Gross Unrealized Gains	8,414	7,896
Securities Held to Maturity, Gross Unrealized Losses	33,506	37,999
Securities Held to Maturity, Fair Value	2,477,420	2,470,117
U.S. Treasury And Government Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	50,000	50,000
Securities Held to Maturity, Gross Unrealized Losses	55	44
Securities Held to Maturity, Fair Value	49,945	49,956
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	734,075	648,093
Securities Held to Maturity, Gross Unrealized Gains	3,345	2,147
Securities Held to Maturity, Gross Unrealized Losses	17,604	20,175
Securities Held to Maturity, Fair Value	719,816	630,065
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	830,522	862,162
Securities Held to Maturity, Gross Unrealized Gains	3,481	4,329
Securities Held to Maturity, Gross Unrealized Losses	1,980	3,068
Securities Held to Maturity, Fair Value	832,023	863,423
Commercial Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	75,722	75,739
Securities Held to Maturity, Gross Unrealized Losses	4,348	4,038
Securities Held to Maturity, Fair Value	71,374	71,701
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	812,193	864,226
Securities Held to Maturity, Gross Unrealized Gains	1,588	1,420
Securities Held to Maturity, Gross Unrealized Losses	9,519	10,674
Securities Held to Maturity, Fair Value	$ 804,262	$ 854,972