Time Deposits (Schedule of Detailed Time Deposits) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Time Deposits [Abstract]
Noninterest-bearing deposits	$ 8,499,027	$ 8,307,497
Interest-bearing retail transaction and savings deposits	8,000,092	8,181,555
Interest-bearing public fund deposits, Public fund transaction and savings deposits	2,622,938	2,763,182
Interest-bearing public fund deposits, Public fund time deposits	383,578	277,136
Total interest-bearing public fund deposits	3,006,516	3,040,318
Retail time deposits	2,416,086	1,906,768
Brokered time deposits	1,228,464	817,064
Total interest-bearing deposits	14,651,158	13,945,705
Total deposits	$ 23,150,185	$ 22,253,202