Securities (Amortized Cost and Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	$ 2,874,454	$ 2,500,220
Securities Held to Maturity, Gross Unrealized Gains	16,297	7,896
Securities Held to Maturity, Gross Unrealized Losses	24,222	37,999
Securities Held to Maturity, Fair Value	2,866,529	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	64	44
Securities Held to Maturity, Fair Value	49,936	49,956
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	730,599	648,093
Securities Held to Maturity, Gross Unrealized Gains	7,205	2,147
Securities Held to Maturity, Gross Unrealized Losses	9,614	20,175
Securities Held to Maturity, Fair Value	728,190	630,065
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	796,190	862,162
Securities Held to Maturity, Gross Unrealized Gains	7,402	4,329
Securities Held to Maturity, Gross Unrealized Losses	1,315	3,068
Securities Held to Maturity, Fair Value	802,277	863,423
Commercial Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	75,705	75,739
Securities Held to Maturity, Gross Unrealized Losses	2,637	4,038
Securities Held to Maturity, Fair Value	73,068	71,701
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	1,221,960	864,226
Securities Held to Maturity, Gross Unrealized Gains	1,690	1,420
Securities Held to Maturity, Gross Unrealized Losses	10,592	10,674
Securities Held to Maturity, Fair Value	$ 1,213,058	$ 854,972