Securities (Securities Held to Maturity with Unrealized Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	$ 401,593	$ 768,589
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	2,660	6,515
Held to maturity, Losses 12 months or longer, Fair Value	1,720,624	1,055,983
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	46,813	22,096
Held to maturity, Total, Fair Value	2,122,217	1,824,572
Held to maturity, Total, Gross Unrealized Losses	49,473	28,611
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	49,521	49,711
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	478	289
Held to maturity, Total, Fair Value	49,521	49,711
Held to maturity, Total, Gross Unrealized Losses	478	289
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	233,469	14,603
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	2,256	19
Held to maturity, Losses 12 months or longer, Fair Value	233,280	230,960
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	7,247	4,226
Held to maturity, Total, Fair Value	466,749	245,563
Held to maturity, Total, Gross Unrealized Losses	9,503	4,245
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	8,815
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	123	99
Held to maturity, Losses 12 months or longer, Fair Value	235,251	230,277
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	5,994	2,591
Held to maturity, Total, Fair Value	325,981	239,092
Held to maturity, Total, Gross Unrealized Losses	6,117	2,690
Commercial Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value		174,882
Held to maturity, Losses less than 12 months, Gross Unrealized Losses		744
Held to maturity, Losses 12 months or longer, Fair Value	305,419	72,499
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	10,882	3,171
Held to maturity, Total, Fair Value	305,419	247,381
Held to maturity, Total, Gross Unrealized Losses	10,882	3,915
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity, Losses less than 12 months, Fair Value	77,394	570,289
Held to maturity, Losses less than 12 months, Gross Unrealized Losses	281	5,653
Held to maturity, Losses 12 months or longer, Fair Value	897,153	472,536
Held to maturity, Losses 12 months or longer, Gross Unrealized Losses	22,212	11,819
Held to maturity, Total, Fair Value	974,547	1,042,825
Held to maturity, Total, Gross Unrealized Losses	$ 22,493	$ 17,472