Securities (Amortized Cost and Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	$ 2,428,432	$ 2,370,388
Securities Held to Maturity, Gross Unrealized Gains	57,009	21,304
Securities Held to Maturity, Gross Unrealized Losses	2,901	15,841
Securities Held to Maturity, Fair Value	2,482,540	2,375,851
US Treasury and Government Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	50,000	50,000
Securities Held to Maturity, Gross Unrealized Gains	860
Securities Held to Maturity, Gross Unrealized Losses		410
Securities Held to Maturity, Fair Value	50,860	49,590
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	541,839	185,890
Securities Held to Maturity, Gross Unrealized Gains	11,182	3,475
Securities Held to Maturity, Gross Unrealized Losses	1,462	1,166
Securities Held to Maturity, Fair Value	551,559	188,199
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	903,703	1,014,135
Securities Held to Maturity, Gross Unrealized Gains	36,200	15,585
Securities Held to Maturity, Gross Unrealized Losses		1,589
Securities Held to Maturity, Fair Value	939,903	1,028,131
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	932,890	1,120,363
Securities Held to Maturity, Gross Unrealized Gains	8,767	2,244
Securities Held to Maturity, Gross Unrealized Losses	1,439	12,676
Securities Held to Maturity, Fair Value	$ 940,218	$ 1,109,931