Bank Call Loans - Summary of Bank Call Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Bank Call Loans [Abstract]
Year-end balance	$ 15,000	$ 118,300
Weighted interest rate (at end of year)	3.43%	2.25%
Maximum balance (at any month-end)	$ 161,800	$ 230,400
Bank Call Loans Average Amount Outstanding	$ 53,271	$ 123,918
Average interest rate (during the year)	2.66%	2.08%