Securities (Amortized Cost and Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	$ 2,497,558	$ 2,370,388
Securities Held to Maturity, Gross Unrealized Gains	72,816	21,304
Securities Held to Maturity, Gross Unrealized Losses	1,290	15,841
Securities Held to Maturity, Fair Value	2,569,084	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	1,047
Securities Held to Maturity, Gross Unrealized Losses		410
Securities Held to Maturity, Fair Value	51,047	49,590
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	496,999	185,890
Securities Held to Maturity, Gross Unrealized Gains	18,158	3,475
Securities Held to Maturity, Gross Unrealized Losses	372	1,166
Securities Held to Maturity, Fair Value	514,785	188,199
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	946,722	1,014,135
Securities Held to Maturity, Gross Unrealized Gains	40,068	15,585
Securities Held to Maturity, Gross Unrealized Losses		1,589
Securities Held to Maturity, Fair Value	986,790	1,028,131
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Total held to maturity securities, Amortized Cost	1,003,837	1,120,363
Securities Held to Maturity, Gross Unrealized Gains	13,543	2,244
Securities Held to Maturity, Gross Unrealized Losses	918	12,676
Securities Held to Maturity, Fair Value	$ 1,016,462	$ 1,109,931