Securities (Securities Held to Maturity with Unrealized Losses) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Losses less than 12 months, Fair Value	$ 8,750	$ 401,593
Held to Maturity, Losses less than 12 months, Gross Unrealized Losses	63	2,660
Held to Maturity, Losses 12 months or longer, Fair Value	1,578,313	1,720,624
Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses	22,935	46,813
Held to Maturity, Total, Fair Value	1,587,063	2,122,217
Held to Maturity, Total, Gross Unrealized Losses	22,998	49,473
U.S. Treasury And Government Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Losses 12 months or longer, Fair Value	49,682	49,521
Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses	317	478
Held to Maturity, Total, Fair Value	49,682	49,521
Held to Maturity, Total, Gross Unrealized Losses	317	478
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Losses less than 12 months, Fair Value	8,750	233,469
Held to Maturity, Losses less than 12 months, Gross Unrealized Losses	63	2,256
Held to Maturity, Losses 12 months or longer, Fair Value	169,931	233,280
Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses	1,663	7,247
Held to Maturity, Total, Fair Value	178,681	466,749
Held to Maturity, Total, Gross Unrealized Losses	1,726	9,503
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Losses less than 12 months, Fair Value		90,730
Held to Maturity, Losses less than 12 months, Gross Unrealized Losses		123
Held to Maturity, Losses 12 months or longer, Fair Value	186,221	235,251
Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses	3,148	5,994
Held to Maturity, Total, Fair Value	186,221	325,981
Held to Maturity, Total, Gross Unrealized Losses	3,148	6,117
Commercial Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Losses 12 months or longer, Fair Value	312,296	305,419
Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses	3,780	10,882
Held to Maturity, Total, Fair Value	312,296	305,419
Held to Maturity, Total, Gross Unrealized Losses	3,780	10,882
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Losses less than 12 months, Fair Value		77,394
Held to Maturity, Losses less than 12 months, Gross Unrealized Losses		281
Held to Maturity, Losses 12 months or longer, Fair Value	860,183	897,153
Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses	14,027	22,212
Held to Maturity, Total, Fair Value	860,183	974,547
Held to Maturity, Total, Gross Unrealized Losses	$ 14,027	$ 22,493