Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH WITHIN THE CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION:
Cash and cash equivalents	$ 1,132,395	$ 1,483,836
Deposits with banks and short-term investments	1,015,872	935,431
Cash deposited with clearing organizations and other segregated cash	37,985	35,539
TOTAL CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	$ 2,186,252	$ 2,454,806	$ 1,941,863	$ 1,607,483