Bank Deposits (Scheduled Maturities of Certificates of Deposit) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Deposits Liabilities Balance Sheet Reported Amounts [Abstract]
Within one year	$ 5,617	$ 438
One to three years	544	148
Three to five years	127
Certificates of deposit, less than $100	6,288	586
Within one year	1,740,855	651
One to three years	193,185	338
Three to five years	29,990
Certificates of deposit, $100 and greater	1,964,030	989
Total certificates of deposit	$ 1,970,318	$ 1,575