Securities (Amortized Cost and Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	$ 2,518,371	$ 2,370,388
Securities Held to Maturity, Gross Unrealized Gains	51,786	21,304
Securities Held to Maturity, Gross Unrealized Losses	3,358	15,841
Securities Held to Maturity, Fair Value	2,566,799	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	672
Securities Held to Maturity, Gross Unrealized Losses		410
Securities Held to Maturity, Fair Value	50,672	49,590
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	417,911	185,890
Securities Held to Maturity, Gross Unrealized Gains	6,270	3,475
Securities Held to Maturity, Gross Unrealized Losses	430	1,166
Securities Held to Maturity, Fair Value	423,751	188,199
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	983,146	1,014,135
Securities Held to Maturity, Gross Unrealized Gains	34,214	15,585
Securities Held to Maturity, Gross Unrealized Losses		1,589
Securities Held to Maturity, Fair Value	1,017,360	1,028,131
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	1,067,314	1,120,363
Securities Held to Maturity, Gross Unrealized Gains	10,630	2,244
Securities Held to Maturity, Gross Unrealized Losses	2,928	12,676
Securities Held to Maturity, Fair Value	$ 1,075,016	$ 1,109,931