Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Abstract]
Cash and due from banks	$ 3,444,971	$ 2,672,290
Securities purchased under agreements to resell	123,611	247,876
Other short-term investment securities	2,957	2,909
Total cash and cash equivalents	$ 3,571,539	$ 2,923,075	$ 2,545,750	$ 1,503,257